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There's no need to have the device open RW while obtaining the readahead value.
The RW open used before caused the CHANGE udev event to be generated if the
WATCH udev rule was set for the underlying device (and that is normally the
case both for non-dm and dm devices by default).
This did not cause any problems before since we were not interested in
*underlying* devices. However, with upcoming changes (autoactivation), we're
watching for events on underlying devices marked as PVs and such a spurious
event could cause the autoactivation code to be triggered. So when trying
to deactivate the volume, we could end up with immediate activation just after
that because of the CHANGE event originated in the WATCH udev rule since the
underlying device was open RW during the deactivation process.
Though maybe a better solution would be to completely filter such spurious
events out of the autoactivation process somehow, it's still useful if there
are as least spurious events generated as possible in the system itself.
Since the function dev_close() has code path, which really could close
file (for unlocked vg) and destroy dev handler, stay on safe side and move
the close few lines later, even our current use case shouldn't trigger
such scenario.
Since the !(dev->flags & DEV_REGULAR) code path just called
dev_name_confirmed() which has just called 'stat()' inside,
remove duplicate second stat() call here.
Before, we used vg_write_lock_held call to determnine the way a device is
opened. Unfortunately, this opened many devices in RW mode when it was not
really necessary. With the OPTIONS+="watch" rule used in the udev rules,
this could fire numerous events while closing such devices (and it caused
useless scans from within udev rules in return).
A common bug we hit with this was with the lvremove command which was unable
to remove the LV since it was being opened from within the udev rules. This
patch should minimize such situations (at least with respect to LVM handling
of devices).
Though there's still a possibility someone will open a device 'outside' in
parallel and fire the event based on the watch rule when closing a device
once opened for RW.
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).
When we are stacking LV over device, which has for some reason
increased read_ahead (e.g. MD RAID), the read_ahead hint
for libdevmapper is wrong (it is zero).
If the calculated read_ahead hint is zero, patch uses read_ahead of underlying device
(if first segment is PV) when setting DM_READ_AHEAD_MINIMUM_FLAG.
Because we are using dev-cache, it also store this value to cache for future use
(if several LVs are over one PV, BLKRAGET is called only once for underlying device.)
This should fix all the reamining problems with readahead mismatch reported
for DM over MD configurations (and similar cases).
* lib/device/dev-io.c (dev_open_flags):
Use log_sys_error after failed stat to report strerror(errno).
Use a slightly different diagnostic to report mismatched device number.
Additional verbosity level -vvvv includes line numbers and backtraces.
Verbose messages now go to stderr not stdout.
Close any stray file descriptors before starting.
Refine partitionable checks for certain device types.
Allow devices/types to override built-ins.
Clear many compiler warnings (i386) & associated bugs - hopefully without
introducing too many new bugs:-) (Same exercise required for other archs.)
Default compilation has optimisation - or else use ./configure --enable-debug
Lots of changes/very little testing so far => there'll be bugs!
Use 'vgcreate -M text' to create a volume group with its metadata stored
in text files. Text format metadata changes should be reasonably atomic,
with a (basic) automatic recovery mechanism if the system crashes while a
change is in progress.
Add a metadata section to lvm.conf to specify multiple directories if
you want (recommended) to keep multiple copies of the metadata (eg on
different filesystems).
e.g. metadata {
dirs = ["/etc/lvm/metadata1","/usr/local/lvm/metadata2"]
}
Plenty of refinements still in the pipeline.
Patrick, can you see if this fixes your cluster syncing problem please ?
If so I'll make it so it only syncs if you have actually written to the
device.
This should be a rare occurrence so the aim is to recover if it's
straightforward to do so, otherwise just to abort the operation.
If people *knowingly* change device names, they should always run vgscan
afterwards.
A few bytes of memory gets leaked inside a pool each time an alias
has to be discarded - it's not worth restructuring the code to reuse it.
More of LVM2 needs updating to pass device objects (or uuids) about
instead of pathnames so that resolution of pathname->object only happens
once per operation.
dev_cache_get() should now always return the *current* device at the path given
dev_name_confirmed() replaces dev_name() whenever it's important to
know that name for the device is still current (ie when opening it).
If the cache doesn't know a current name, the function fails.
dev_open() guarantees that the file descriptor returned is for the dev_t
of the device structure it was passed.
o When opening device, return error if its cached name is incorrect (eg if
it's changed since the cache was generated). This prevents use until
the cache is rebuilt (eg with vgscan). Doesn't catch every case.
o Changed disk-rep to use these
o if NDEBUG is not defined the dev_cache will check for open devices on
teardown.
I was hoping this would speed things up. But I'm still getting:
reti:/home/joe/sistina/LVM2/tools# time ./lvm vgchange -a n
Volume group vg0 successfully changed
real 0m5.751s
user 0m0.060s
sys 0m0.070s
even though I have only 1 device with the vg on it passing the filters.
