Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
/*
2014-03-17 13:38:38 +04:00
* Copyright ( C ) 2011 , 2013 , 2014 Red Hat , Inc .
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
*
* This library is free software ; you can redistribute it and / or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation ; either
* version 2.1 of the License , or ( at your option ) any later version .
*
* This library is distributed in the hope that it will be useful ,
* but WITHOUT ANY WARRANTY ; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE . See the GNU
* Lesser General Public License for more details .
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library ; If not , see
* < http : //www.gnu.org/licenses/>.
*/
# include <config.h>
# include <signal.h>
2020-02-24 00:02:26 +03:00
# include <unistd.h>
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
# include <sys/stat.h>
# include "testutils.h"
2013-05-09 22:59:04 +04:00
# include "virfile.h"
2012-12-12 21:59:27 +04:00
# include "virlog.h"
2020-02-25 13:01:09 +03:00
# include "virutil.h"
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
# include "virlockspace.h"
# define VIR_FROM_THIS VIR_FROM_RPC
2014-02-28 16:16:17 +04:00
VIR_LOG_INIT ( " tests.lockspacetest " ) ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
# define LOCKSPACE_DIR abs_builddir " / virlockspacedata"
2019-10-14 15:45:03 +03:00
static int testLockSpaceCreate ( const void * args G_GNUC_UNUSED )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
{
2021-03-11 10:16:13 +03:00
virLockSpace * lockspace ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
int ret = - 1 ;
rmdir ( LOCKSPACE_DIR ) ;
2013-09-25 18:31:48 +04:00
if ( ! ( lockspace = virLockSpaceNew ( LOCKSPACE_DIR ) ) )
goto cleanup ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
if ( ! virFileIsDir ( LOCKSPACE_DIR ) )
goto cleanup ;
ret = 0 ;
2014-03-25 10:53:44 +04:00
cleanup :
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
virLockSpaceFree ( lockspace ) ;
rmdir ( LOCKSPACE_DIR ) ;
return ret ;
}
2019-10-14 15:45:03 +03:00
static int testLockSpaceResourceLifecycle ( const void * args G_GNUC_UNUSED )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
{
2021-03-11 10:16:13 +03:00
virLockSpace * lockspace ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
int ret = - 1 ;
rmdir ( LOCKSPACE_DIR ) ;
2013-09-25 18:31:48 +04:00
if ( ! ( lockspace = virLockSpaceNew ( LOCKSPACE_DIR ) ) )
goto cleanup ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
if ( ! virFileIsDir ( LOCKSPACE_DIR ) )
goto cleanup ;
if ( virLockSpaceCreateResource ( lockspace , " foo " ) < 0 )
goto cleanup ;
if ( ! virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
if ( virLockSpaceDeleteResource ( lockspace , " foo " ) < 0 )
goto cleanup ;
if ( virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
ret = 0 ;
2014-03-25 10:53:44 +04:00
cleanup :
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
virLockSpaceFree ( lockspace ) ;
rmdir ( LOCKSPACE_DIR ) ;
return ret ;
}
2019-10-14 15:45:03 +03:00
static int testLockSpaceResourceLockExcl ( const void * args G_GNUC_UNUSED )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
{
2021-03-11 10:16:13 +03:00
virLockSpace * lockspace ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
int ret = - 1 ;
rmdir ( LOCKSPACE_DIR ) ;
2013-09-25 18:31:48 +04:00
if ( ! ( lockspace = virLockSpaceNew ( LOCKSPACE_DIR ) ) )
goto cleanup ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
if ( ! virFileIsDir ( LOCKSPACE_DIR ) )
goto cleanup ;
if ( virLockSpaceCreateResource ( lockspace , " foo " ) < 0 )
goto cleanup ;
2018-10-02 16:10:22 +03:00
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) , 0 ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
goto cleanup ;
if ( ! virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
2018-10-02 16:10:22 +03:00
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) , 0 ) = = 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
goto cleanup ;
if ( virLockSpaceDeleteResource ( lockspace , " foo " ) = = 0 )
goto cleanup ;
if ( virLockSpaceReleaseResource ( lockspace , " foo " , geteuid ( ) ) < 0 )
goto cleanup ;
if ( virLockSpaceDeleteResource ( lockspace , " foo " ) < 0 )
goto cleanup ;
if ( virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
ret = 0 ;
2014-03-25 10:53:44 +04:00
cleanup :
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
virLockSpaceFree ( lockspace ) ;
rmdir ( LOCKSPACE_DIR ) ;
return ret ;
}
2019-10-14 15:45:03 +03:00
static int testLockSpaceResourceLockExclAuto ( const void * args G_GNUC_UNUSED )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
{
2021-03-11 10:16:13 +03:00
virLockSpace * lockspace ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
int ret = - 1 ;
rmdir ( LOCKSPACE_DIR ) ;
2013-09-25 18:31:48 +04:00
if ( ! ( lockspace = virLockSpaceNew ( LOCKSPACE_DIR ) ) )
goto cleanup ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
if ( ! virFileIsDir ( LOCKSPACE_DIR ) )
goto cleanup ;
if ( virLockSpaceCreateResource ( lockspace , " foo " ) < 0 )
goto cleanup ;
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) ,
VIR_LOCK_SPACE_ACQUIRE_AUTOCREATE ) < 0 )
goto cleanup ;
if ( ! virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
if ( virLockSpaceReleaseResource ( lockspace , " foo " , geteuid ( ) ) < 0 )
goto cleanup ;
if ( virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
ret = 0 ;
2014-03-25 10:53:44 +04:00
cleanup :
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
virLockSpaceFree ( lockspace ) ;
rmdir ( LOCKSPACE_DIR ) ;
return ret ;
}
2019-10-14 15:45:03 +03:00
static int testLockSpaceResourceLockShr ( const void * args G_GNUC_UNUSED )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
{
2021-03-11 10:16:13 +03:00
virLockSpace * lockspace ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
int ret = - 1 ;
rmdir ( LOCKSPACE_DIR ) ;
2013-09-25 18:31:48 +04:00
if ( ! ( lockspace = virLockSpaceNew ( LOCKSPACE_DIR ) ) )
goto cleanup ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
if ( ! virFileIsDir ( LOCKSPACE_DIR ) )
goto cleanup ;
if ( virLockSpaceCreateResource ( lockspace , " foo " ) < 0 )
goto cleanup ;
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) ,
VIR_LOCK_SPACE_ACQUIRE_SHARED ) < 0 )
goto cleanup ;
2018-10-02 16:10:22 +03:00
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) , 0 ) = = 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
goto cleanup ;
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) ,
VIR_LOCK_SPACE_ACQUIRE_SHARED ) < 0 )
goto cleanup ;
if ( virLockSpaceDeleteResource ( lockspace , " foo " ) = = 0 )
goto cleanup ;
if ( virLockSpaceReleaseResource ( lockspace , " foo " , geteuid ( ) ) < 0 )
goto cleanup ;
if ( virLockSpaceDeleteResource ( lockspace , " foo " ) = = 0 )
goto cleanup ;
if ( virLockSpaceReleaseResource ( lockspace , " foo " , geteuid ( ) ) < 0 )
goto cleanup ;
if ( virLockSpaceDeleteResource ( lockspace , " foo " ) < 0 )
goto cleanup ;
if ( virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
ret = 0 ;
2014-03-25 10:53:44 +04:00
cleanup :
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
virLockSpaceFree ( lockspace ) ;
rmdir ( LOCKSPACE_DIR ) ;
return ret ;
}
2019-10-14 15:45:03 +03:00
static int testLockSpaceResourceLockShrAuto ( const void * args G_GNUC_UNUSED )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
{
2021-03-11 10:16:13 +03:00
virLockSpace * lockspace ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
int ret = - 1 ;
rmdir ( LOCKSPACE_DIR ) ;
2013-09-25 18:31:48 +04:00
if ( ! ( lockspace = virLockSpaceNew ( LOCKSPACE_DIR ) ) )
goto cleanup ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
if ( ! virFileIsDir ( LOCKSPACE_DIR ) )
goto cleanup ;
if ( virLockSpaceCreateResource ( lockspace , " foo " ) < 0 )
goto cleanup ;
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) ,
VIR_LOCK_SPACE_ACQUIRE_SHARED |
VIR_LOCK_SPACE_ACQUIRE_AUTOCREATE ) < 0 )
goto cleanup ;
if ( ! virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) ,
VIR_LOCK_SPACE_ACQUIRE_AUTOCREATE ) = = 0 )
goto cleanup ;
if ( ! virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
if ( virLockSpaceAcquireResource ( lockspace , " foo " , geteuid ( ) ,
VIR_LOCK_SPACE_ACQUIRE_SHARED |
VIR_LOCK_SPACE_ACQUIRE_AUTOCREATE ) < 0 )
goto cleanup ;
if ( ! virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
if ( virLockSpaceReleaseResource ( lockspace , " foo " , geteuid ( ) ) < 0 )
goto cleanup ;
if ( ! virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
if ( virLockSpaceReleaseResource ( lockspace , " foo " , geteuid ( ) ) < 0 )
goto cleanup ;
if ( virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
ret = 0 ;
2014-03-25 10:53:44 +04:00
cleanup :
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
virLockSpaceFree ( lockspace ) ;
rmdir ( LOCKSPACE_DIR ) ;
return ret ;
}
2019-10-14 15:45:03 +03:00
static int testLockSpaceResourceLockPath ( const void * args G_GNUC_UNUSED )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
{
2021-03-11 10:16:13 +03:00
virLockSpace * lockspace ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
int ret = - 1 ;
rmdir ( LOCKSPACE_DIR ) ;
2013-09-25 18:31:48 +04:00
if ( ! ( lockspace = virLockSpaceNew ( NULL ) ) )
goto cleanup ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
2020-01-17 14:21:29 +03:00
if ( g_mkdir ( LOCKSPACE_DIR , 0700 ) < 0 )
2013-01-03 23:16:18 +04:00
goto cleanup ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
if ( virLockSpaceCreateResource ( lockspace , LOCKSPACE_DIR " /foo " ) < 0 )
goto cleanup ;
2018-10-02 16:10:22 +03:00
if ( virLockSpaceAcquireResource ( lockspace , LOCKSPACE_DIR " /foo " , geteuid ( ) , 0 ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
goto cleanup ;
if ( ! virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
2018-10-02 16:10:22 +03:00
if ( virLockSpaceAcquireResource ( lockspace , LOCKSPACE_DIR " /foo " , geteuid ( ) , 0 ) = = 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
goto cleanup ;
if ( virLockSpaceDeleteResource ( lockspace , LOCKSPACE_DIR " /foo " ) = = 0 )
goto cleanup ;
if ( virLockSpaceReleaseResource ( lockspace , LOCKSPACE_DIR " /foo " , geteuid ( ) ) < 0 )
goto cleanup ;
if ( virLockSpaceDeleteResource ( lockspace , LOCKSPACE_DIR " /foo " ) < 0 )
goto cleanup ;
if ( virFileExists ( LOCKSPACE_DIR " /foo " ) )
goto cleanup ;
ret = 0 ;
2014-03-25 10:53:44 +04:00
cleanup :
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
virLockSpaceFree ( lockspace ) ;
rmdir ( LOCKSPACE_DIR ) ;
return ret ;
}
static int
mymain ( void )
{
int ret = 0 ;
2020-01-22 20:59:39 +03:00
# ifndef WIN32
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
signal ( SIGPIPE , SIG_IGN ) ;
2020-01-22 20:59:39 +03:00
# endif /* WIN32 */
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
2016-05-26 18:01:50 +03:00
if ( virTestRun ( " Lockspace creation " , testLockSpaceCreate , NULL ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
ret = - 1 ;
2016-05-26 18:01:50 +03:00
if ( virTestRun ( " Lockspace res lifecycle " , testLockSpaceResourceLifecycle , NULL ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
ret = - 1 ;
2016-05-26 18:01:50 +03:00
if ( virTestRun ( " Lockspace res lock excl " , testLockSpaceResourceLockExcl , NULL ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
ret = - 1 ;
2016-05-26 18:01:50 +03:00
if ( virTestRun ( " Lockspace res lock shr " , testLockSpaceResourceLockShr , NULL ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
ret = - 1 ;
2016-05-26 18:01:50 +03:00
if ( virTestRun ( " Lockspace res lock excl auto " , testLockSpaceResourceLockExclAuto , NULL ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
ret = - 1 ;
2016-05-26 18:01:50 +03:00
if ( virTestRun ( " Lockspace res lock shr auto " , testLockSpaceResourceLockShrAuto , NULL ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
ret = - 1 ;
2016-05-26 18:01:50 +03:00
if ( virTestRun ( " Lockspace res full path " , testLockSpaceResourceLockPath , NULL ) < 0 )
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
ret = - 1 ;
2014-03-17 13:38:38 +04:00
return ret = = 0 ? EXIT_SUCCESS : EXIT_FAILURE ;
Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence
threadA: fd1 = open("foo")
threadB: fd2 = open("foo")
threadA: virFileLock(fd1)
threadB: virFileLock(fd2)
threadB: close(fd2)
you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.
To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace". This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.
NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.
eg to lock /var/lib/libvirt/images/foo.img the application
might do
virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
lockname = md5sum("/var/lib/libvirt/images/foo.img");
virLockSpaceAcquireLock(lockspace, lockname);
NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.
It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg
virLockSpacePtr lockspace = virLockSpaceNew(NULL);
virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");
This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-08-02 20:02:40 +04:00
}
2017-03-29 17:45:42 +03:00
VIR_TEST_MAIN ( mymain )
