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Previously, a command would only rescan a lockd VG
when lvmetad returned the "vg_invalid" flag indicating
that the cached copy was invalid (which is done by
lvmlockd.) This is still the only usual reason for
rescanning a lockd VG, but two new special cases are
added where we also do the rescan:
. When the --shared option is used to display lockd VGs
from hosts not using lvmlockd. This is the same case
as using --foreign to display foreign VGs, but --shared
was missing the corresponding bits to rescan the VGs.
. When a lockd VG is allowed to be read for displaying
after failing to acquire the lock from lvmlockd. In
this case, the usual mechanism for validating the
cache is missed, so assume the cache would have been
invalidated. (This had been a previous todo item
that was lost during other cleanup.)
These were long-standing todos that were lost track of.
This makes lvmlockd removal steps for dlm VGs closely match
sanlock VGs. Because dlm lockspaces are not required to be
stopped on all hosts before vgremove, there is an extra bit
for dlm lockspaces, where a flag is set in the VG lock lvb
indicating that the VG was removed. If other hosts happen
to use the VG lock they will see this flag and stop their
lockspace.
Remove the existing lock type using the same functions
used to remove the lockd components during vgremove.
This results in a "clean" VG and lvmlockd state after
the vgchange, i.e. no bits left over from previous
lock type.
When vgremove is used to remove multiple VGs in one command,
e.g. vgremove foo bar, the first VG (foo) that is removed
may have held the sanlock global lock. In this case,
do not continue removing further VGs (bar) without the
global lock.
This adds the infrastructure, code paths, error reporting,
etc. to handle storage errors, or storage loss, under the
sanlock leases in a VG that is being used. The loss of
storage means sanlock cannot renew its leases, which means
that the host needs to stop using the shared VG before its
leases expire.
This still requires manually shutting down a VG that has
lost lease storage, e.g. unmounting file systems,
deactivating LVs in the VG. The next step is to
automatically use a command like blkdeactivate to do that.
When a command is flagged with NO_METADATA_PROCESSING flag, it means
such command does not process any metadata and hence it doens't require
lvmetad, lvmpolld and it can get away with no locking too. These are
mostly simple commands (like lvmconfig/dumpconfig, version, types,
segtypes and other builtin commands that do not process metadata
in any way).
At first, when lvm command is executed, create toolcontext without
initializing connections (lvmetad,lvmpolld) and without initializing
filters (which depend on connections init). Instead, delay this
initialization until we know we need this. That is, until the
lvm_run_command fn is called in which we know what the actual
command to run is and hence we can avoid any connection, filter
or locking initiliazation for commands that would not make use
of it anyway.
For all the other create_toolcontext calls, we keep the original
behaviour - the filters and connections are initialized together
with the toolcontext.
This tries harder to avoid creating duplicate global locks in
sanlock VGs by refusing to create a new sanlock VG with a
global lock if other sanlock VGs exist that may have a gl.
There is no longer an "enable" option for the global lock,
so remove the bit of code that was checking for it. It
was an optional variation anyway, and not one that was likely
to be used.
Also update the corresponding comment describing global lock
creation.
When lvmlockd is compiled without support for one of the
lock managers (sanlock or dlm), and a command tries to use
one of them, explain that in the error message.
When lvm is built without lvmlockd support, vgcreate using a
shared lock type would succeed and create a local VG (the
--shared option was effectively ignored). Make it fail.
Fix the same issue when using vgchange to change a VG to a
shared lock type.
Make the error messages consistent.
When --nolocking is used (by vgs, lvs, pvs):
. don't use lvmlockd at all (set use_lvmlockd to 0)
. allow lockd VGs to be read
When --readonly is used (by vgs, lvs, pvs, vgdisplay, lvdisplay,
pvdisplay, lvmdiskscan, lvscan, pvscan, vgcfgbackup):
. skip actual lvmlockd locking calls
. allow lockd VGs to be read
. check that only shared gl/vg locks are being requested
(even though the actually locking is being skipped)
. check that no LV locks are requested, because no LVs
should be activated or used in readonly mode
. disable using lvmetad so VGs are read from disk
It is important to note the limited commands that accept
the --nolocking and --readonly options, i.e. no commands
that change/write a VG or change/activate LVs accept these
options, only commands that read VGs.
There are at least a couple instances where
the lock_args check does not work correctly,
(listed in the comment), so disable the
NULL check for lock_args until those are
resolved.
including the allow_override_lock_modes setting.
It was not possible to override default lock modes any longer,
since the command line options had already been removed.
A mechanism will probably be required later that puts part of
this back.
Take a local file lock to prevent concurrent activation/deactivation of LVs.
Thin/cache types and an extension for cluster support are excluded for
now.
'lvchange -ay $lv' and 'lvchange -an $lv' should no longer cause trouble
if issued concurrently: the new lock should make sure they
activate/deactivate $lv one-after-the-other, instead of overlapping.
(If anyone wants to experiment with the cluster patch, please get in touch.)
Instead of sending repeatedly LOCAL_SYNC commands to clvmds
like 'lvs', rememeber the last sent commmand, and if there was no other
clvmd command, drop this redundant SYNC call message.
The problem has started with commit:
56cab8cc03
This introduced correct synchronisation of name, when user requests to know
open_count (needs to wait for udev), however it is also executed for
read-only cases like 'lvs' command.
For now implement very simple solution, which is only monitoring
outgoing clvmd command, and when sequence of LOCAL sync names are
recognized, they are skipped automatically.
TODO:
Future solution might move this variable info 'cmd_context' and
use 'needs_sync' flag also i.e. in file locking code.
These settings don't have any default value predefined:
log/file
log/activate_file
global/library_dir
This settings has default value but not yet declared in config_settings.h:
global/locking_library (default is DEFAULT_LOCKING_LIB)
When lvm2 command forks, it calls reset_locking(),
which as an unwanted side effect unlinked lock file from filesystem.
Patch changes the behavior to just close locked file descriptor
in children - so the lock is being still properly hold in the parent.
Correct return code of activate_lv_excl().
Function is not supposed to return activation state of
activated volume, but return code of the operation.
Since i.e. when activation filter is allowing to activate
volume on current system, it is still success even though
no volume is activated.
Add LV_TEMPORARY flag for LVs with limited existence during command
execution. Such LVs are temporary in way that they need to be activated,
some action done and then removed immediately. Such LVs are just like
any normal LV - the only difference is that they are removed during
LVM command execution. This is also the case for LVs representing
future pool metadata spare LVs which we need to initialize by using
the usual LV before they are declared as pool metadata spare.
We can optimize some other parts like udev to do a better job if
it knows that the LV is temporary and any processing on it is just
useless.
This flag is orthogonal to LV_NOSCAN flag introduced recently
as LV_NOSCAN flag is primarily used to mark an LV for the scanning
to be avoided before the zeroing of the device happens. The LV_TEMPORARY
flag makes a difference between a full-fledged LV visible in the system
and the LV just used as a temporary overlay for some action that needs to
be done on underlying PVs.
For example: lvcreate --thinpool POOL --zero n -L 1G vg
- first, the usual LV is created to do a clean up for pool metadata
spare. The LV is activated, zeroed, deactivated.
- between "activated" and "zeroed" stage, the LV_NOSCAN flag is used
to avoid any scanning in udev
- betwen "zeroed" and "deactivated" stage, we need to avoid the WATCH
udev rule, but since the LV is just a usual LV, we can't make a
difference. The LV_TEMPORARY internal LV flag helps here. If we
create the LV with this flag, the DM_UDEV_DISABLE_DISK_RULES
and DM_UDEV_DISABLE_OTHER_RULES flag are set (just like as it is
with "invisible" and non-top-level LVs) - udev is directed to
skip WATCH rule use.
- if the LV_TEMPORARY flag was not used, there would normally be
a WATCH event generated once the LV is closed after "zeroed"
stage. This will make problems with immediated deactivation that
follows.
A common scenario is during new LV creation when we need to wipe the
newly created LV and avoid any udev scanning before this stage otherwise
it could cause the device (the LV) to be claimed by some other subsystem
for which there were stale metadata within LV data.
This patch adds possibility to mark the LV we're just about to wipe with
a flag that gets passed to udev via DM_COOKIE as a subsystem specific
flag - DM_SUBSYSTEM_UDEV_FLAG0 (in this case the subsystem is "LVM")
so LVM udev rules will take care of handling that.
According to bug 995193, if a volume group
1) contains a mirror
2) is clustered
3) 'locking_type' = 0 is used
then it is not possible to remove the 'c'luster flag from the VG. This
is due to the way _lv_is_active behaves.
We shouldn't allow the cluster flag to be flipped unless the mirrors in
the cluster are not active. This is because different kernel modules
are used depending on whether a mirror is cluster or not. When we
attempt to see if the mirror is active, we first check locally. If it
is not, then we attempt to check for remotely active instances if the VG
is clustered. Since the no_lock locking type is LCK_CLUSTERED, but does
not implement 'query_resource', remote_lock_held will always return an
error in this case. An error from remove_lock_held is treated as though
the lock _is_ held (i.e. the LV is active remotely). This blocks the
cluster flag from changing.
The solution is to implement 'query_resource' for the no_lock type. It
will report a message and return 1. This will allow _lv_is_active to
function properly. The LV would be considered not active remotely and
the VG can change its flag.
Fix and improve handling on sigint.
Always check for signal presence *before* calling of command,
so it will not call the command when break was hit.
If the command has been finished succesfully there is
no problem to mark the command ok and not report interrupt at all.
Fix cuple related stack; reports and assignments.
This ties the two preceding changes together, actually using the "ondisk"
version of VG metadata instead of calling into lvmcache when activating
volumes. The cache hooks are still used as a fallback, because we don't have an
uncached scanning API yet.
Previously, we have relied on UUIDs alone, and on lvmcache to make getting a
"new copy" of VG metadata fast. If the code which triggers the activation has
the correct VG metadata at hand (the version which is currently on disk), it can
now hand it to the activation code directly.
For example, the old call and reference:
find_config_tree_str(cmd, "devices/dir", DEFAULT_DEV_DIR)
...now becomes:
find_config_tree_str(cmd, devices_dir_CFG)
So we're referring to the named configuration ID instead
of passing the configuration path and the default value
is taken from central config definition in config_settings.h
automatically.
Activation on remote node should be tried only if it is masked by tags
locally (like when hosttags enabled, IOW activate_lv_excl_local()
doesn't return error.)
Introduced change caused that lvchange -aey succeeded even if volume was
activated exclusively remotely.
This patch to the suspend code - like the similar change for resume -
queries the lock mode of a cluster volume and records whether it is active
exclusively. This is necessary for suspend due to the possibility of
preloading targets. Failure to check to exclusivity causes the cluster target
of an exclusively activated mirror to be used when converting - rather than
the single machine target.
LVM- prefix.
Try harder not to leave stray empty devices around (locally or remotely) when
reverting changes after failures while there are inactive tables.
This was the intended behaviour, as described in the lvchange man page, so you
have complete control through volume_list in lvm.conf, but the code seems to
have been treating -ae as local-only for a very long time.
leaving behind the LVM-specific parts of the code (convenience wrappers that
handle `struct device` and `struct cmd_context`, basically). A number of
functions have been renamed (in addition to getting a dm_ prefix) -- namely,
all of the config interface now has a dm_config_ prefix.
Move the free_vg() to vg.c and replace free_vg with release_vg
and make the _free_vg internal.
Patch is needed for sharing VG in vginfo cache so the release_vg function name
is a better fit here.
(here clvmd crashed in the middle of operation),
lock is not removed from cache - here is one example:
locking/cluster_locking.c:497 Locking VG V_vg_test UN (VG) (0x6)
locking/cluster_locking.c:113 Error writing data to clvmd: Broken pipe
locking/locking.c:399 <backtrace>
locking/locking.c:461 <backtrace>
Internal error: Volume Group vg_test was not unlocked
Code should always remove lock info from lvmcache and update counters
on unlock, even if unlock fails.
Today, we use "suppress_messages" flag (set internally in init_locking fn based
on 'ignorelockingfailure() && getenv("LVM_SUPPRESS_LOCKING_FAILURE_MESSAGES")'.
This way, we can suppress high level messages like "File-based locking
initialisation failed" or "Internal cluster locking initialisation failed".
However, each locking has its own sequence of initialization steps and these
could log some errors as well. It's quite misleading for the user to see such
errors and warnings if the "--sysinit" is used (and so the ignorelockingfailure
&& LVM_SUPPRESS_LOCKING_FAILURE_MESSAGES environment variable). Errors and
warnings from these intermediary steps should be suppressed as well if requested.
This patch propagates the "suppress_messages" flag deeper into locking init
functions. I've also added these flags for other locking types for consistency,
though it's not actually used for no_locking and readonly_locking.
are affected by the move. (Currently it's possible for I/O to become
trapped between suspended devices amongst other problems.
The current fix was selected so as to minimise the testing surface. I
hope eventually to replace it with a cleaner one that extends the
deptree code.
Some lvconvert scenarios still suffer from related problems.
Fix 2 more functions sending cluster messages to avoid passing uninitilised bytes
and compensate 1 extra byte attached to the message from the clvm_header.args[1]
member variable.
New strategy for memory locking to decrease the number of call to
to un/lock memory when processing critical lvm functions.
Introducing functions for critical section.
Inside the critical section - memory is always locked.
When leaving the critical section, the memory stays locked
until memlock_unlock() is called - this happens with
sync_local_dev_names() and sync_dev_names() function call.
memlock_reset() is needed to reset locking numbers after fork
(polldaemon).
The patch itself is mostly rename:
memlock_inc -> critical_section_inc
memlock_dec -> critical_section_dec
memlock -> critical_section
Daemons (clmvd, dmevent) are using memlock_daemon_inc&dec
(mlockall()) thus they will never release or relock memory they've
already locked memory.
Macros sync_local_dev_names() and sync_dev_names() are functions.
It's better for debugging - and also we do not need to add memlock.h
to locking.h header (for memlock_unlock() prototyp).
results in clvmd deadlock
When a logical volume is activated exclusively in a cluster, the
local (non-cluster-aware) target is used. However, when creating
a snapshot on the exclusive LV, the resulting suspend/resume fails
to load the appropriate device-mapper table - instead loading the
cluster-aware target.
This patch adds an 'exclusive' parameter to the pertinent resume
functions to allow for the right target type to be loaded.
activated.
In order to achieve this, we need to be able to query whether
the origin is active exclusively (a condition of being able to
add an exclusive snapshot).
Once we are able to query the exclusive activation of an LV, we
can safely create/activate the snapshot.
A change to 'hold_lock' was also made so that a request to aquire
a WRITE lock did not replace an EX lock, which is already a form
of write lock.
Remove temporaly added fs_unlock() calls to fix clmvd usablity.
Now when the message passing is properly working - they are no longer needed.
Simplify no_locking check for VG unlock - as message is always send
for all targets - clustered & non-clustered.
Thanks to CLVMD_CMD_SYNC_NAMES propagation fix the message passing started
to work. So starts to send a message before the VG is unlocked.
Removing also implicit sync in VG unlock from clmvd as now the message
is delievered and processed in do_command().
Also add support for this new message into external locking
and mask this event from further processing.
This is better way how to fix clustered synchronization with udev.
As the code for message passing needs fixed - put currently
fs_unlock() after every active/deactive command in clvmd to
ensure nodes are properly created in time.
There was no effect from having this wrong yet, because the
tree of callers only ever cared about the answer to the first
condition (!response), which determines whether a lock is
held or not. Correct responses, however, are needed soon.
Instead of implicitly syncing udev operation in clustered and
file locking code - call synchronization directly in lock_vol() when
the operation unlocks VG
The problem is missing implicit fs_unlock() in the no_locking code.
This is used with --sysinit on read-only filesystem locking dir.
In this case vgchange -ay could exit before all udev nodes are properly
synchronised and may cause problems with accessing such node right after
vgchange --sysinint command is finished.
Add test case for vgchange --sysinit.
Improve condition within lock_vol so we are not calling extra unlock
if the volume just has been deactivated.
Patch uses lck_type and replaces negative 'and' condition to more
readable 'or' condition.
Few missing strace traces added.
Stop calling fs_unlock() from lv_de/activate().
Start using internal lvm fs cookie for dm_tree.
Stop directly calling dm_udev_wait() and
dm_tree_set/get_cookie() from activate code -
it's now called through fs_unlock() function.
Add lvm_do_fs_unlock()
Call fs_unlock() when unlocking vg where implicit unlock solves the
problem also for cluster - thus no extra command for clustering
environment is required - only lvm_do_fs_unlock() function is added
to call lvm's fs_unlock() while holding lvm_lock mutex in clvmd.
Add fs_unlock() also to set_lv() so the command waits until devices
are ready for regular open (i.e. wiping its begining).
Move fs_unlock() prototype to activation.h to keep fs.h private
in lib/activate dir and not expose other functions from this header.
Detect existence of new SELinux selabel interface during configure.
Use new dm_prepare_selinux_context instead of dm_set_selinux_context.
We should set the SELinux context before the actual file system object creation.
The new dm_prepare_selinux_context function sets this using the selabel_lookup
fn in conjuction with the setfscreatecon fn. If selinux/label.h interface
(that should be a part of the selinux library) is not found during configure,
we fallback to the original matchpathcon function instead.
Ignore snapshots when performing mirror recovery beneath an origin.
Pass LCK_ORIGIN_ONLY flag around cluster.
Add suspend_lv_origin and resume_lv_origin using LCK_ORIGIN_ONLY.
Code is mixing up internal DLM and LVM definitions of lock
modes and flags.
OpenAIS and singlenode locking do not depend on DLM but
code currently cannot be compiled without libdlm.h!
LCK_* flags is LVM abstraction, used through all the code.
Only low-level backend (clvmd-cman etc) should use DLM definitions,
also this code should do all needed conversions.
Because there are two DLM flags used in generic code
(NOQUEUE, CONVERT) we define it similar way like lock modes.
(So all needed binary-compatible flags are on one place in locking.h)
(Further code cleaning still needed, though:-)
A shortcut for --ignorelockingfailure, --ignoremonitoring, --poll n options
and LVM_SUPPRESS_LOCKING_FAILURE_MESSAGES environment variable used all at
once in initialisation scripts (e.g. rc.sysinit or initrd).
Target install_dm_plugin installs files to libdir/device-mapper.
Target install_lvm2_plugin installs files to libdir/lvm2.
Both targets creates relative links to libdir to keep the code
compatible with current dlopen handling.
Once we will be able to read plugins from subdir, links
could be removed.
Patch is inspired by Debian's extra patch.
- removes OWNER & GROUP make vars they are parts of INSTALL command.
- adds INSTALL_PROGRAM for executable, uses $(INSTALL)
- adds INSTALL_DATA for non-executable data, uses ($INSTALL)
- adds INSTALL_WDATA for writable non-executable data, uses ($INSTALL)
- adds configure option --enable-write_install - to support
installatin of writable files used by distribution
- replaces usage of ifeq @LIB_SUFFIX@ with $(LIB_SUFFIX)
- installs .a files from static builds without executable flag
- installs .a files to $(usrlibdir) instead of $(libdir)
- installs all static binaries to $(staticdir)
- create .so links for devel package in $(usrlibdir) instead of
$(libdir)
- makes .so and .so.LIB_VERSION files within builddir
- removes VERSIONED_SHLIB and created versioned LIB_SHARED automagicaly
- install LIB_SHARED via install_lib_shared target
- install plugins via install_lib_shared_plugin target
- prints whole 'install' command during installation instead of less
informative "Installing $(something) $(somewhere)"
- install multiple man pages with one INSTALL command
- use DISTCLEAN_TARGETS instead of creating multiple distclean targets
Usage of VPATH makes troubles when used within $(builddir).
Not only source files are being found through VPATH,
but targets as well. (make --debug=v)
Thus if user builds the code in $(srcdir) and also in some $(builddir)
he gets mangled results as some generated files (i.e. .export.sym)
are 'reused' from $(srcdir) instead of $(builddir).
This patch switches to use vpath were we could explicitly name
suffixes that should be looked via vpath - we must take care,
we do not generate files with these suffixes:
.c, .in, .po, .exported_symbols
Because we have now strong rule for lock ordering:
- VG locks must be taken in alphabetical order
- ORPHAN locks must be the last
vgs_locked() is now not needed.
This fixes problem with orphan locking, e.g.
vgremove VG1 | vgremove VG2
lock(VG1) | lock(VG2)
lock(ORPHAN) | lock(ORPHAN) -> fail, non-blocking
https://bugzilla.redhat.com/show_bug.cgi?id=578413
(More similar places in code.)
clvmd's do_lock_lv() already properly controls dmeventd monitoring based
on LCK_DMEVENTD_MONITOR_MODE in lock_flags -- though one small fix was
needed for this to work: _lock_for_cluster() must treat
dmeventd_monitor_mode()'s return as a tri-state value.
Also cleanup do_lock_lv() to:
- explicitly init_dmeventd_monitor() based on LCK_DMEVENTD_MONITOR_MODE
- no longer reset init_dmeventd_monitor() to default at the end of
do_lock_lv() -- it is unnecessary
This patch adds a new implementation of locking function instead
of mlockall() that may lock way too much memory (>100MB).
New function instead uses mlock() system call and selectively locks
memory areas from /proc/self/maps trying to avoid locking areas
unused during lock-ed state.
Patch also adds struct cmd_context to all memlock() calls to have
access to configuration.
For backward compatibility functionality of mlockall()
is preserved with "activation/use_mlockall" flag.
As a simple check, locking and unlocking counts the amount of memory
and compares whether values are matching.
more descriptive message if locking fails instead of
"Locking type -1 initialisation failed."
Use read-only locking instead of misleading ignorelocking option
in message.
This patch tries to correctly track changes in lvmcache related to commit/revert.
For vg_commit: if there is cached precommitted metadata, after successfull commit
these metadata must be tracked as committed.
For vg_revert: remote nodes must drop precommitted metadata and its flag in lvmcache.
(N.B. Patch do not touch LV locks here in any way.)
All this machinery is needed to properly solve remote node cache invalidaton which
cause several problems recently observed.
Lock mode is int masked by LCK_TYPE_MASK, always.
Patch also remove uneccessary masking lock flag on sender side,
if masking is needed, it is don on client side already.
- Add drop_precommitted flag to force drop precommitted metadata
- add lvmcache_commit_metadata() which upgrades precommitted metadata in cache
No functional change in this patch - just preparation for following change.
And decode flags in humar readable form in client.
And clean some trailing whitespaces.
No functional change in this patch (only debugging messages changed).
Patch should not cause any problems, only real change is
removing LCK_LOCAL bit from lock type flag, it is never used there.
(LCK_LOCAL is part arg[1] bits anyway.)
(This affects only cluster locking because only cluster
locking module set LCK_PRE_MEMLOCK.)
With currect code you get
# vgchange -a n
Internal error: _memlock_count has dropped below 0.
when using cluster locking.
It is caused by _unlock_memory calls here
if ((flags & (LCK_SCOPE_MASK | LCK_TYPE_MASK)) == LCK_LV_RESUME)
memlock_dec();
Unfortunately it is also (wrongly) called in immediate unlock
(when LCK_HOLD is not set) from lock_vol
(LCK_UNLOCK is misinterpreted as LCK_LV_RESUME).
Avoid this by comparing original flags and provide memlock
code type of operation (suspend/resume).
Add a new constraint that vgname locks must be obtained in
alphabetical order. At this point, we have test coverage for
the 3 commands affected - vgsplit, vgmerge, and vgrename.
Tests have been updated to cover these commands.
Going forward any command or library call that must obtain
more than one vgname lock must do so in alphabetical order.
Future patches will update lvm2app to enforce this ordering.
Author: Dave Wysochanski <dwysocha@redhat.com>
We provide a lock type that behaves like no_locking, but is not
clustered. Moreover, it also forbids any write locks. This magically (and
consistently) prevents use of clustered VGs, or changing local VGs with
--ignorelockingfailure. As a bonus, we can remove the special hacks in a few
places. Of course, people looking for trouble can always set their locking_type
to 0 to override.
Current code, when need to ensure that volume is not
active on remote node, it need to try to exclusive
activate volume.
Patch adds simple clvmd command which queries all nodes
for lock for given resource.
The lock type is returned in reply in text.
(But code currently uses CR and EX modes only.)
As a simplification to the tools and further liblvm, this patch pushes
the setting of NON_BLOCKING lock flag inside the lock_vol() call.
The policy we set is if any existing VGs are currently locked, we
set the NON_BLOCKING flag.
Should be no functional change.
Run backup of metadata on remote nodes in the
same place like local node - when calling backup().
Introduce backup_locally() which calls only
local backup if needed.
Remote backup is now trigerred by LCK_VG_BACKUP flag
combination (special VG lock).
This lock type will call check_current_backup()
(including backup_locally() call) and updates
metadata on all nodes.
(Patch fixes non-functional remote backup,
current call during VG lock never triggers.)
Since now, all code reading volume group is responsible for releasing
the memory allocated by calling vg_release(vg).
(For simplicity of use, vg_releae can be called for vg == NULL,
the same logic like free(NULL)).
Also providing simple macro for unlocking & releasing in one step,
tools usualy uses this approach.
The global memory pool (cmd->mem) should be used only for global
physical volume operations.
This patch have to be applied with all subsequent patches to complete
memory pool per vg logic.
Using separate memory pool has quite bit memory saving impact when
using large VGs, this is mainly needed when we have to use
preallocated and locked memory (and should not overflow from that
memory space).
Very simple / crude method of removing 'is_static' from initialization.
Why should we require an application tell us whether it is linked
statically or dynamically to libLVM? If the application is linked
statically, but libraries exist and dlopen() calls succeed, why
do we care if it's statically linked?
