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It doesn't make sense to test or warn about the region count until
the stats handle has been listed: at this point it may or may not
contain valid information (but is guaranteed to be correct after
the list).
As we start refactoring the code to break dependencies (see doc/refactoring.txt),
I want us to use full paths in the includes (eg, #include "base/data-struct/list.h").
This makes it more obvious when we're breaking abstraction boundaries, eg, including a file in
metadata/ from base/
When function dm_stats_populate() returns 0 it's an error and needs
log_error() message - function can't have 'success' returning 0 or
error without reasons.
API for strtod() or strtoul() needs reset of errno, before it's being
called. So add missing resets in missing places and some also some
errno validation for out-of-range numbers.
It's not an error to attempt to update regions from an fd that has
been truncated (or otherwise no longer has any allocated extents):
in this case, the call should remove all regions corresponding to
the group, and return an empty region table.
Use log_sys_error rather than log_error if execvp() fails:
/mnt/redhat/xdoio.13752.XIORQ: Created new group with 2 region(s) as group ID 0.
# execvp() failed.
vs:
/var/lib/libvirt/images/rhel7-vm1.qcow2: Created new group with 884 region(s) as group ID 0.
dmfilemapd: execvp failed: No such file or directory
Require that the path argument to dmfilemapd be an absolute path
and document this in tool output, libdevmapper.h and dmfilemapd.8.
The check is also enforced by dm_stats_start_filemapd() to avoid
forking a new process with an invalid path argument.
Test for NULL in dm_stats_destroy() and return immediately if
the struct dm_stats pointer is NULL (similar to free(NULL)).
This simplifies cleanup code which otherwise needs to:
out:
if (dms)
dm_stats_destroy(dms);
return;
Older compilers are not able to determine that although group_id
is only assigned in one branch of a conditional, it is never used
used when the other branch is taken:
libdm-stats.c:3319: warning: "group_id" may be used uninitialized in this function
Avoid this by always initialising the variable when it is
declared.
Add a daemon that can be launched to monitor a group of regions
corresponding to the extents of a file, and to update the regions as the
file's allocation changes.
The daemon is intended to be started from a library interface, but can
also be run from the command line:
dmfilemapd <fd> <group_id> <path> <mode> [<foreground>[<log_level>]]
Where fd is a file descriptor open on the mapped file, group_id is the
group identifier of the mapped group and mode is either "inode" or
"path". E.g.:
# dmfilemapd 3 0 vm.img inode 1 3 3<vm.img
...
If foreground is non-zero, the daemon will not fork to run in the
background. If verbose is non-zero, libdm and daemon log messages will
be printed.
It is possible for the group identifier to change when regions are
re-mapped: this occurs when the group leader is deleted (regroup=1 in
dm_stats_update_regions_from_fd()), and another region is created before
the daemon has a chance to recreate the leader region.
The operation is inherently racey since there is currently no way to
atomically move or resize a dm_stats region while retaining its
region_id.
Detect this condition and update the group_id value stored in the
filemap monitor.
A function is also provided in the the stats API to launch the filemap
monitoring daemon:
int dm_stats_start_filemapd(int fd, uint64_t group_id, const char *path,
dm_filemapd_mode_t mode, unsigned foreground,
unsigned verbose);
This carries out the first fork and execs dmfilemapd with the arguments
specified.
A dm_filemapd_mode_t value is specified by the mode argument: either
DM_FILEMAPD_FOLLOW_INODE, or DM_FILEMAPD_FOLLOW_PATH. A helper function,
dm_filemapd_mode_from_string(), is provided to parse a string containing
a valid mode name into the appropriate dm_filemapd_mode_t value.
It's not an error to call dm_stats_group_present() on a handle
that contains no regions.
This causes dmfilemap to log a false backtrace during shutdown
if all regions are removed from the corresponding device:
exiting _filemap_monitor_get_events() with deleted=0, check=0
waiting for FILEMAPD_WAIT
dm message (253:1) [ opencount flush ] @stats_list dmstats [32768] (*1)
<backtrace>
Filemap group removed: exiting.
Change this to only emit a backtrace if the handle is NULL.
Add a call to update the regions corresponding to a file mapped
group of regions. The regions to be updated must be grouped, to
allow us to correctly identify extents that have been deallocated
since the map was created.
Tables are built of the file extents, and the extents currently
mapped to dmstats regions: if a region no longer has a matching
file extent, it is deleted, and new regions are created for any
file extents without a matching region.
The FIEMAP call returns extents that are currently in-memory (or
journaled) and awaiting allocation in the file system. These have
the FIEMAP_EXTENT_UNKNOWN | FIEMAP_EXTENT_DELALLOC flag bits set
in the fe_flags field - these extents are skipped until they
have a known disk location.
Since it is possile for the 0th extent of the file to have been
deallocated this must also handle the possible deletion and
re-creation of the group leader: if no other region allocation
is taking place the group identifier will not change.
If the group_id passed to _stats_group_id_present is equal to the
special value DM_STATS_GROUP_NOT_PRESENT there is no need to perform
any further tests: return false immediately.
Call _stats_regions_destroy() from dm_stats_list() if dms->regions
is non-NULL. This avoids leaking any pool allocations and ensures
the handle is in a known state: if an error occurs during the list,
dms->regions will be NULL and the handle will appear empty.
If FIEMAP returns a single extent after the first call, no extent
boundary is detected and the first extent is not counted by the
normal mechanism.
In this case, increment nr_extents at the same time the extent is
added to the region table, before returning.
It's useful to be able to specify a minimum number of bits for a
new bitmap parsed from a list, for e.g. to allow for expansing a
group without needing to copy/reallocate the bitmap.
Add a backwards compatible symbol for programs linked against old
versions of the library.
Split out the loop that iterates over each batch of FIEMAP
extent data from the function that sets up and calls the ioctl
to reduce nesting and simplify local variable use:
_stats_get_extents_for_file()
-> _stats_map_extents()
The _stats_map_extents() function is responsible for detecting
eof and extent boundaries and adding whole, allocated extents
to the file extent table for region creation.
