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lvm2 is caching DM nodes with the use of DM_LIST_DEVICES ioctl().
And tried to preserve the cached structure for the same list,
however there was 1 case where cache was empty, and new LIST ioctl
returned some elements - if this DM table change has happened
in the moment of 'scanning' and locking - lvm2 has then continued
to use 'invalid' empty cache.
Fix by capturing this missed case and update cache properly.
TODO: we could possibly use plain memcmp() with previous ioctl result.
Since we started to use DM cache now also for basic checks
whether the DM devices is present in DM table, this cache
now needs to be actually refreshed when the LOCK is taken.
This hiddenly happend if there was enabled 'scan_lvs' however
still not at the right place.
Move this explicit cache update call right after the moment
vg_read grabs the lock.
TODO: in the optimal case, we should mark the 'cache invalid'
and later refresh this cache, when the first reader appears,
but since this would be large patch, do this little fix step patch
first and improve performance later.
With existing code, the cache was working only to the 2nd. locking.
So i.e. when 'lvs' scans system with more then one VG, the caching
was effectively not working.
Update the code, so the label invalidate code is able to update DM
cache - so whenever we take a new lock - we will refresh the cache.
TODO: the refresh ATM does a very simple compare of old a new list
of cached DM device, and with the first spotted difference, it just
fallback to the full rebuild of DM cache - with large amount of active
devices this might not the most efficient way....
The cmd struct is now required in many more functions, and
it's added as a function arg for most direct dev-cache function
calls. The cmd struct is added to struct device (dev->cmd) so
that it can be accessed in many other cases where dev-cache
functions are being called from places where getting the cmd
struct is too difficult.
The dm devs cache is separate from the ordinary dev cache,
so give the function names distinct prefixes, using
"dm_devs_cache" to prefix dm devs cache functions.
When a PV is stacked on an LV, the PV needs to be
dropped from bcache before the LV is processed.
The LV can be found in dev-cache using its name
rather than the devno.
The list of dm devs was in the cmd struct and had a
different lifetime than the radix trees referencing
those dm devs. Now the list and radix trees are
created and destroyed together.
In the context of dm, 'device' refers to a dm device, but
in the context of lvm, 'device' refers to struct device.
Change some lvm function names to make that difference clearer.
dev_manager_get_device_list() -> dev_manager_get_dm_active_devices()
get_device_list() -> get_dm_active_devices()
device_get_uuid() -> dev_dm_uuid(), devno_dm_uuid()
For large device sets our dm_hash can produce larger amounf of mapping
collision and we would need to further increase our has size.
So instead use the radix_tree code which is immune agains growing size
of devices and uses memory more effiecently to store all the paths.
Instead of less efficient 'btree' switch dev_cache to use
radix_tree, that is generating more efficient tree mapping.
Some direct use of btree iteration replace with our dev_iter code.
Move the code around caching active dm device devno, name and uuid
from device_mapper/libdm-iface to dev_cache file - as libdm layer
cares about 'decoding' ioctl data from kernel and caching for use by
lvm stays within lvm.
Introduce:
dev_cache_update_dm_devs
dev_cache_get_dm_dev_by_devno
dev_cache_get_dm_dev_by_uuid
Use radix_tree for searching.
Size of these hashes was quite small, so raise the size of
hashed entries to reduce amount of hash collistion.
Select some unique/unused number for hash_create below 8192.
Replace call to get_dm_uuid_from_sysfs() with use of
device_get_uuid() which gets the same information,
but instead of several syscalls it need either 1 or even 0
when the information is cached with newer kernels.
For better use of cached data located within cmd_context,
pass this structure from the top level function.
Also add missing '_' for static _dev_cache_index_devs.
No other change here.
Skip scan and stat() for dirs and nodes within known /dev/ paths,
where no block devices are located.
Also strlen(_cache.dev_dir) just once.
TODO: add more dirs to _no_scan (configurable via lvm.conf ?)
If lvm.conf has use_devicesfile=0 and /etc/lvm/device/system.devices
exists, then rename it to system.devices-unused.YYYYMMDD.HHMMSS.
This prevents an old, incorrect system.devices from being used in
the future if lvm.conf is changed to use_devicesfile=1.
