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Although we expect min_chunk_size to be 32bit value, for
large size of caches it might be useful to do calcs 64bit.
So to avoid doing shift as signed 32bit - use unsigned 64bit
from the start.
reporting fields (-o) directly from kernel:
writecache_total_blocks
writecache_free_blocks
writecache_writeback_blocks
writecache_error
The data_percent field shows used cache blocks / total cache blocks.
Until we resolve reshape for 'stacked' devices, we need to disable it.
So users can no longer reshape i.e. thin-pool data volumes, causing
ATM bad thin-pool problems.
After the VG lock is taken for vg_read, reread the mda_header
and compare the metadata text offset and checksum to what was
seen during label scan. If it is unchanged, then the metadata
has not changed since the label scan, and the metadata does not
need to be reread under the lock for command processing.
For commands that do not make changes (e.g. reporting), the
mda_header is reread and checked on one mda to decide if the
full metadata rereading can be skipped. For other commands
(e.g. modifying the vg) the mda_header is reread and checked
from all PVs. (These could probably just check one mda also.)
dev_unset_last_byte() must be called while the fd is still valid.
After a write error, dev_unset_last_byte() must be called before
closing the dev and resetting the fd.
In the write error path, dev_unset_last_byte() was being called
after label_scan_invalidate() which meant that it would not unset
the last_byte values.
After a write error, dev_unset_last_byte() is now called in
dev_write_bytes() before label_scan_invalidate(), instead of by
the caller of dev_write_bytes().
In the common case of a successful write, the sequence is still:
dev_set_last_byte(); dev_write_bytes(); dev_unset_last_byte();
Signed-off-by: Zhao Heming <heming.zhao@suse.com>
When resizing 2 volumes like thin-pool and it's metadata and they
would be of a different type - command would be actually expecting
both LVs being of a same segtype - and would throw an error in
case they are different.
This patch fixes is by setting a new segtype from last segment of
2nd. extented device.
Also it fixes the possible 'percentage' extension setup that
might have been used for 'primary' volume - while the 'secondary'
LV always goes with direct size - as we do not support 'percentage'
setup for them
This affects maily usage of thin-pool where the extension of
thin-pool data size may also lead to extension of metadata size.
Instead of checking all LVs in a VG - do just a direct copy of LVs
from the existing list ->segs_using_thin_lv.
TODO: maybe it could be better to expose seg_list to /tools...
The resume of 'released' 'COW' should preceed the resume of origin.
The fact we need to do the sequence differently for merge was
cause by bugs fixed in 2 previous commits - so we no longer need
to recognize 'merging' and we should always go with single
sequence.
The importance of this order is - to properly remove '-real' device
from origin LV. When COW is activated as 2nd. '-real' device is
kept in table as it cannot be removed during 1st. resume of origin,
and later activation of COW LV no longer builds tree associated
with origin LV.
When a cachevol LV is attached, have the LV keep it's lock
allocated. The lock on the cachevol won't be used while
it's attached. When the cachevol is split a new lock does
not need to be allocated. (Applies to cachevol usage by
both dm-cache and dm-writecache.)
When LV gets cached and uses cache-pool - such cache-pool
will now get _cpool suffix automatically.
Thus 'Pool' column for cached LV will now show either _cvol
or _cpool LV.
Before 'archive()' is called, lvm2 must not touch/modify metadata.
So move setting CACHE_VOL related flags past this point.
Also make sure reading of cache segtype always restores this
flag properly (even if compatible flag would be lost).
Since code is using -cdata and -cmeta UUID suffixes, it does not need
any new 'extra' ID to be generated and stored in metadata.
Since introduce of new 'segtype' cache+CACHE_USES_CACHEVOL we can
safely assume 'new' cache with cachevol will now be created
without extra metadata_id and data_id in metadata.
For backward compatibility, code still reads them in case older
version of metadata have them - so it still should be able
to activate such volumes.
Bonus is lowered size of lv structure used to store info about LV
(noticable with big volume groups).
The first part of a cachevol LV is used for metadata,
and the rest of the space is used for data. The
division of space between metadata and data depends
on the total size of the cachevol.
The previous division gave more space than needed to
metadata, it was:
cachevol size 8M to 128M -> metadata size 16M *
cachevol size 128M to 1G -> metadata size 32M
cachevol size 1G and up -> metadata size 64M
(* if this resulted in over half the LV used as
metadata, then half the cachevol would be used
for metadata, and the other half for data.)
The division of space now gives less space to
metadata, it is:
cachevol size 8M to 16M -> metadata size 4M
cachevol size 16M to 4G -> metadata size 8M
cachevol size 4G to 16G -> metadata size 16M
cachevol size 16G to 32G -> metadata size 32M
cachevol size 32G and up -> metadata size 64M
When a VG contains some LVs with unknown segtypes, the user
should still be allowed to activate other LVs in the VG that
are understood.
$ lvs foo
WARNING: Unrecognised flag CACHE_USES_CACHEVOL in segment type cache+CACHE_USES_CACHEVOL.
WARNING: Unrecognised segment type cache+CACHE_USES_CACHEVOL
LV VG Attr LSize
lvol0 foo -wi------- 4.00m
other foo vwi---u--- 48.00m
$ lvcreate -l1 foo
WARNING: Unrecognised flag CACHE_USES_CACHEVOL in segment type cache+CACHE_USES_CACHEVOL.
WARNING: Unrecognised segment type cache+CACHE_USES_CACHEVOL
Cannot change VG foo with unknown segments in it!
Cannot process volume group foo
$ lvchange -ay foo/lvol0
WARNING: Unrecognised flag CACHE_USES_CACHEVOL in segment type cache+CACHE_USES_CACHEVOL.
WARNING: Unrecognised segment type cache+CACHE_USES_CACHEVOL
$ lvchange -ay foo/other
WARNING: Unrecognised flag CACHE_USES_CACHEVOL in segment type cache+CACHE_USES_CACHEVOL.
WARNING: Unrecognised segment type cache+CACHE_USES_CACHEVOL
Refusing activation of LV foo/other containing an unrecognised segment.
$ lvs foo
WARNING: Unrecognised flag CACHE_USES_CACHEVOL in segment type cache+CACHE_USES_CACHEVOL.
WARNING: Unrecognised segment type cache+CACHE_USES_CACHEVOL
LV VG Attr LSize
lvol0 foo -wi-a----- 4.00m
other foo vwi---u--- 48.00m
A cachevol LV had the CACHE_VOL status flag in metadata,
and the cache LV using it had no new flag. This caused
problems if the new metadata was used by an old version
of lvm. An old version of lvm would have two problems
processing the new metadata:
. The old lvm would return an error when reading the VG
metadata when it saw the unknown CACHE_VOL status flag.
. The old lvm would return an error when reading the VG
metadata because it would not find an expected cache pool
attached to the cache LV (since the cache LV had a
cachevol attached instead.)
Change the use of flags:
. Change the CACHE_VOL flag to be a COMPATIBLE flag (instead
of a STATUS flag) so that old versions will not fail when
they see it.
. When a cache LV is using a cachevol, the cache LV gets
a new SEGTYPE flag CACHE_USES_CACHEVOL. This flag is
appended to the segtype name, so that old lvm versions
will fail to use the LV because of an unknown segtype,
as opposed to failing to read the VG.
Let vgck --updatemetadata repair cases where different mdas
hold indepedently valid but unmatching copies of the metadata,
i.e. different text metadata checksums or text metadata sizes.
Avoid checking 'lv_is_active()' since special LV types does this
validation anyway what calling _percent() function and call it
ONLY when none of special types is queried.
This restores support for VDO resize (as with support for
separate VDO pool activation, plain query for lv_is_active()
is not working in this case).
- use internal CACHE_VOL flag on cachevol LV
- add suffixes to dm uuids for internal LVs
- display appropriate letters in the LV attr field
- display writecache's cachevol in lvs output
. For dm-cache in writethrough, always allow splitcache,
whether the cache is missing PVs or not.
. For dm-cache in writeback, if the cache is missing PVs,
allow splitcache with force and yes.
. For dm-writecache, if the cache is missing PVs,
allow splitcache with force and yes.
Enhance 'activation' experience for VDO pool to more closely match
what happens for thin-pools where we do use a 'fake' LV to keep pool
running even when no thinLVs are active. This gives user a choice
whether he want to keep thin-pool running (wihout possibly lenghty
activation/deactivation process)
As we do plan to support multple VDO LVs to be mapped into a single VDO,
we want to give user same experience and 'use-patter' as with thin-pools.
This patch gives option to activate VDO pool only without activating
VDO LV.
Also due to 'fake' layering LV we can protect usage of VDO pool from
command like 'mkfs' which do require exlusive access to the volume,
which is no longer possible.
Note: VDO pool contains 1024 initial sectors as 'empty' header - such
header is also exposed in layered LV (as read-only LV).
For blkid we are indentified as LV with UUID suffix - thus private DM
device of lvm2 - so we do not need to store any extra info in this
header space (aka zero is good enough).
When an online PV completed a VG, the standard
activation functions were used to activate the VG.
These functions use a full scan of all devs.
When many pvscans are run during startup and need
to activate many VGs, scanning all devs from all
the pvscans can take a long time.
Optimize VG activation in pvscan to scan only the
devs in the VG being activated. This makes use of
the online file info that was used to determine
the VG was complete.
The downside of this approach is that pvscan activation
will not detect duplicate PVs and block activation,
where a normal activation command (which scans all
devices) would.
Fixes a regression from commit ba7ff96faf
"improve reading and repairing vg metadata"
where the error path for a vg name with invalid
charaters was missing an error flag, which led
to the caller not recognizing an error occured.
Previously, an error flag was hidden in the old
_vg_make_handle function.
New udev in rawhide seems to be 'dropping' udev rule operations for devices
that are no longer existing - while this is 'probably' a bug - it's
revealing moments in lvm2 that likely should not run in a single
transaction and we should wait for a cookie before submitting more work.
TODO: it seem more 'error' paths should always include synchronization
before starting deactivating 'just activated' devices.
We should probably figure out some 'automatic' solution for this instead
of placing sync_local_dev_name() all over the place...
Support internal removal of 'cache origin' volume - which we
do not normally expose to a user - however internal processing
loops may hit this condition (depending on order of list LVs).
So when this operation is internally requested - we automatically
try to remove it's 'holding' LV (cache LV) - which will also
remove the origin.
Drop the 'cluster-only' optimization so we do resume ALL device
before we try to wait on cookie before 'removal' operation.
It's more correct order of operation - alhtough possibly slightly
less efficient - but until we have correct list of operations
'in-progress' we can't do anything better.
Usually md components are eliminated in label scan and/or
duplicate resolution, but they could sometimes get into
the vg_read stage, where set_pv_devices compares the
device to the PV.
If set_pv_devices runs an md component check and finds
one, vg_read should eliminate the components.
In set_pv_devices, run an md component check always
if the PV is smaller than the device (this is not
very common.) If the PV is larger than the device,
(more common), do the component check when the config
setting is "auto" (the default).
Avoid having PVs with different logical block sizes in the same VG.
This prevents LVs from having mixed block sizes, which can produce
file system errors.
The new config setting devices/allow_mixed_block_sizes (default 0)
can be changed to 1 to return to the unrestricted mode.
This check was mistakenly removed when shifting code in commit
"separate code for setting devices from metadata parsing".
Put it back with some new conditions.
The exported VG checking/enforcement was scattered and
inconsistent. This centralizes it and makes it consistent,
following the existing approach for foreign and shared
VGs/PVs, which are very similar to exported VGs/PVs.
The access policy that now applies to foreign/shared/exported
VGs/PVs, is that if a foreign/shared/exported VG/PV is named
on the command line (i.e. explicitly requested by the user),
and the command is not permitted to operate on it because it
is foreign/shared/exported, then an access error is reported
and the command exits with an error. But, if the command is
processing all VGs/PVs, and happens to come across a
foreign/shared/exported VG/PV (that is not explicitly named on
the command line), then the command silently skips it and does
not produce an error.
A command using tags or --select handles inaccessible VGs/PVs
the same way as a command processing all VGs/PVs, and will
not report/return errors if these inaccessible VGs/PVs exist.
The new policy fixes the exit codes on a somewhat random set of
commands that previously exited with an error if they were
looking at all VGs/PVs and an exported VG existed on the system.
There should be no change to which commands are allowed/disallowed
on exported VGs/PVs.
Certain LV commands (lvs/lvdisplay/lvscan) would previously not
display LVs from an exported VG (for unknown reasons). This has
not changed. The lvm fullreport command would previously report
info about an exported VG but not about the LVs in it. This
has changed to include all info from the exported VG.
When vg_read rescans devices with the intention of
writing the VG, the label rescan can open the devs
RW so they do not need to be closed and reopened
RW in dev_write_bytes.
Previously the VG metadata description field (which contains
the command line) was only included in backup/archive copies
of the metadata. Now also include it in the metadata written
to the metadata areas.
The way that this command now uses the global lock
followed by a label scan, it can simply check if the
new VG name exists, and if not lock it and create it.
The fact that vg repair is implemented as a part of vg read
has led to a messy and complicated implementation of vg_read,
and limited and uncontrolled repair capability. This splits
read and repair apart.
Summary
-------
- take all kinds of various repairs out of vg_read
- vg_read no longer writes anything
- vg_read now simply reads and returns vg metadata
- vg_read ignores bad or old copies of metadata
- vg_read proceeds with a single good copy of metadata
- improve error checks and handling when reading
- keep track of bad (corrupt) copies of metadata in lvmcache
- keep track of old (seqno) copies of metadata in lvmcache
- keep track of outdated PVs in lvmcache
- vg_write will do basic repairs
- new command vgck --updatemetdata will do all repairs
Details
-------
- In scan, do not delete dev from lvmcache if reading/processing fails;
the dev is still present, and removing it makes it look like the dev
is not there. Records are now kept about the problems with each PV
so they be fixed/repaired in the appropriate places.
- In scan, record a bad mda on failure, and delete the mda from
mda in use list so it will not be used by vg_read or vg_write,
only by repair.
- In scan, succeed if any good mda on a device is found, instead of
failing if any is bad. The bad/old copies of metadata should not
interfere with normal usage while good copies can be used.
- In scan, add a record of old mdas in lvmcache for later, do not repair
them while reading, and do not let them prevent us from finding and
using a good copy of metadata from elsewhere. One result is that
"inconsistent metadata" is no longer a read error, but instead a
record in lvmcache that can be addressed separate from the read.
- Treat a dev with no good mdas like a dev with no mdas, which is an
existing case we already handle.
- Don't use a fake vg "handle" for returning an error from vg_read,
or the vg_read_error function for getting that error number;
just return null if the vg cannot be read or used, and an error_flags
arg with flags set for the specific kind of error (which can be used
later for determining the kind of repair.)
- Saving an original copy of the vg metadata, for purposes of reverting
a write, is now done explicitly in vg_read instead of being hidden in
the vg_make_handle function.
- When a vg is not accessible due to "access restrictions" but is
otherwise fine, return the vg through the new error_vg arg so that
process_each_pv can skip the PVs in the VG while processing.
(This is a temporary accomodation for the way process_each_pv
tracks which devs have been looked at, and can be dropped later
when process_each_pv implementation dev tracking is changed.)
- vg_read does not try to fix or recover a vg, but now just reads the
metadata, checks access restrictions and returns it.
(Checking access restrictions might be better done outside of vg_read,
but this is a later improvement.)
- _vg_read now simply makes one attempt to read metadata from
each mda, and uses the most recent copy to return to the caller
in the form of a 'vg' struct.
(bad mdas were excluded during the scan and are not retried)
(old mdas were not excluded during scan and are retried here)
- vg_read uses _vg_read to get the latest copy of metadata from mdas,
and then makes various checks against it to produce warnings,
and to check if VG access is allowed (access restrictions include:
writable, foreign, shared, clustered, missing pvs).
- Things that were previously silently/automatically written by vg_read
that are now done by vg_write, based on the records made in lvmcache
during the scan and read:
. clearing the missing flag
. updating old copies of metadata
. clearing outdated pvs
. updating pv header flags
- Bad/corrupt metadata are now repaired; they were not before.
Test changes
------------
- A read command no longer writes the VG to repair it, so add a write
command to do a repair.
(inconsistent-metadata, unlost-pv)
- When a missing PV is removed from a VG, and then the device is
enabled again, vgck --updatemetadata is needed to clear the
outdated PV before it can be used again, where it wasn't before.
(lvconvert-repair-policy, lvconvert-repair-raid, lvconvert-repair,
mirror-vgreduce-removemissing, pv-ext-flags, unlost-pv)
Reading bad/old metadata
------------------------
- "bad metadata": the mda_header or metadata text has invalid fields
or can't be parsed by lvm. This is a form of corruption that would
not be caused by known failure scenarios. A checksum error is
typically included among the errors reported.
- "old metadata": a valid copy of the metadata that has a smaller seqno
than other copies of the metadata. This can happen if the device
failed, or io failed, or lvm failed while commiting new metadata
to all the metadata areas. Old metadata on a PV that has been
removed from the VG is the "outdated" case below.
When a VG has some PVs with bad/old metadata, lvm can simply ignore
the bad/old copies, and use a good copy. This is why there are
multiple copies of the metadata -- so it's available even when some
of the copies cannot be used. The bad/old copies do not have to be
repaired before the VG can be used (the repair can happen later.)
A PV with no good copies of the metadata simply falls back to being
treated like a PV with no mdas; a common and harmless configuration.
When bad/old metadata exists, lvm warns the user about it, and
suggests repairing it using a new metadata repair command.
Bad metadata in particular is something that users will want to
investigate and repair themselves, since it should not happen and
may indicate some other problem that needs to be fixed.
PVs with bad/old metadata are not the same as missing devices.
Missing devices will block various kinds of VG modification or
activation, but bad/old metadata will not.
Previously, lvm would attempt to repair bad/old metadata whenever
it was read. This was unnecessary since lvm does not require every
copy of the metadata to be used. It would also hide potential
problems that should be investigated by the user. It was also
dangerous in cases where the VG was on shared storage. The user
is now allowed to investigate potential problems and decide how
and when to repair them.
Repairing bad/old metadata
--------------------------
When label scan sees bad metadata in an mda, that mda is removed
from the lvmcache info->mdas list. This means that vg_read will
skip it, and not attempt to read/process it again. If it was
the only in-use mda on a PV, that PV is treated like a PV with
no mdas. It also means that vg_write will also skip the bad mda,
and not attempt to write new metadata to it. The only way to
repair bad metadata is with the metadata repair command.
When label scan sees old metadata in an mda, that mda is kept
in the lvmcache info->mdas list. This means that vg_read will
read/process it again, and likely see the same mismatch with
the other copies of the metadata. Like the label_scan, the
vg_read will simply ignore the old copy of the metadata and
use the latest copy. If the command is modifying the vg
(e.g. lvcreate), then vg_write, which writes new metadata to
every mda on info->mdas, will write the new metadata to the
mda that had the old version. If successful, this will resolve
the old metadata problem (without needing to run a metadata
repair command.)
Outdated PVs
------------
An outdated PV is a PV that has an old copy of VG metadata
that shows it is a member of the VG, but the latest copy of
the VG metadata does not include this PV. This happens if
the PV is disconnected, vgreduce --removemissing is run to
remove the PV from the VG, then the PV is reconnected.
In this case, the outdated PV needs have its outdated metadata
removed and the PV used flag needs to be cleared. This repair
will be done by the subsequent repair command. It is also done
if vgremove is run on the VG.
MISSING PVs
-----------
When a device is missing, most commands will refuse to modify
the VG. This is the simple case. More complicated is when
a command is allowed to modify the VG while it is missing a
device.
When a VG is written while a device is missing for one of it's PVs,
the VG metadata is written to disk with the MISSING flag on the PV
with the missing device. When the VG is next used, it is treated
as if the PV with the MISSING flag still has a missing device, even
if that device has reappeared.
If all LVs that were using a PV with the MISSING flag are removed
or repaired so that the MISSING PV is no longer used, then the
next time the VG metadata is written, the MISSING flag will be
dropped.
Alternative methods of clearing the MISSING flag are:
vgreduce --removemissing will remove PVs with missing devices,
or PVs with the MISSING flag where the device has reappeared.
vgextend --restoremissing will clear the MISSING flag on PVs
where the device has reappeared, allowing the VG to be used
normally. This must be done with caution since the reappeared
device may have old data that is inconsistent with data on other PVs.
Bad mda repair
--------------
The new command:
vgck --updatemetadata VG
first uses vg_write to repair old metadata, and other basic
issues mentioned above (old metadata, outdated PVs, pv_header
flags, MISSING_PV flags). It will also go further and repair
bad metadata:
. text metadata that has a bad checksum
. text metadata that is not parsable
. corrupt mda_header checksum and version fields
(To keep a clean diff, #if 0 is added around functions that
are replaced by new code. These commented functions are
removed by the following commit.)
uses vg_write to correct more common or less severe issues,
and also adds the ability to repair some metadata corruption
that couldn't be handled previously.
and implement it based on a device, not based
on a pv struct (which is not available when the
device is not a part of the vg.)
currently only the vgremove command wipes outdated
pvs until more advanced recovery is added in a
subsequent commit
The vg read and vg write cases need to update lvmcache
differently, so create separate functions for them.
The read case now handles checking for outdated mdas
and moves them aside into a new list to be repaired in
a subsequent commit.
The existing comment was desribing the correct behavior,
but the code didn't match. The commit is successful if
one mda was committed. Making it depend on the result of
the internal lvmcache update was wrong.
mda's that cannot be processed by lvm because of
some corruption can be kept on a separate list.
These will be used for more advanced repair in a
subsequent commit.
When reading metadata headers and text, use a new set
of flags to identify specific errors that are seen.
These will be used for more advanced repair in a
subsequent commit.
Use the recently added dump routines to produce the
old/traditional pvck output, and remove the code that
had been used for that.
The validation/checking done by the new routines means
that new lines prefixed with CHECK are printed for
incorrect values.
Recent kernel version from kernel commit:
de7180ff908b2bc0342e832dbdaa9a5f1ecaa33a
started to report in cache status line new flag:
no_discard_passdown
Whenever lvm spots unknown status it reports:
Unknown feature in status:
So add reconginzing this feature flag and also report this with
'lvs -o+kernel_discards'
When no_discard_passdown is found in status 'nopassdown' gets reported
for this field (roughly matching what we report for thin-pools).
There have been two file locks used to protect lvm
"global state": "ORPHANS" and "GLOBAL".
Commands that used the ORPHAN flock in exclusive mode:
pvcreate, pvremove, vgcreate, vgextend, vgremove,
vgcfgrestore
Commands that used the ORPHAN flock in shared mode:
vgimportclone, pvs, pvscan, pvresize, pvmove,
pvdisplay, pvchange, fullreport
Commands that used the GLOBAL flock in exclusive mode:
pvchange, pvscan, vgimportclone, vgscan
Commands that used the GLOBAL flock in shared mode:
pvscan --cache, pvs
The ORPHAN lock covers the important cases of serializing
the use of orphan PVs. It also partially covers the
reporting of orphan PVs (although not correctly as
explained below.)
The GLOBAL lock doesn't seem to have a clear purpose
(it may have eroded over time.)
Neither lock correctly protects the VG namespace, or
orphan PV properties.
To simplify and correct these issues, the two separate
flocks are combined into the one GLOBAL flock, and this flock
is used from the locking sites that are in place for the
lvmlockd global lock.
The logic behind the lvmlockd (distributed) global lock is
that any command that changes "global state" needs to take
the global lock in ex mode. Global state in lvm is: the list
of VG names, the set of orphan PVs, and any properties of
orphan PVs. Reading this global state can use the global lock
in sh mode to ensure it doesn't change while being reported.
The locking of global state now looks like:
lockd_global()
previously named lockd_gl(), acquires the distributed
global lock through lvmlockd. This is unchanged.
It serializes distributed lvm commands that are changing
global state. This is a no-op when lvmlockd is not in use.
lockf_global()
acquires an flock on a local file. It serializes local lvm
commands that are changing global state.
lock_global()
first calls lockf_global() to acquire the local flock for
global state, and if this succeeds, it calls lockd_global()
to acquire the distributed lock for global state.
Replace instances of lockd_gl() with lock_global(), so that the
existing sites for lvmlockd global state locking are now also
used for local file locking of global state. Remove the previous
file locking calls lock_vol(GLOBAL) and lock_vol(ORPHAN).
The following commands which change global state are now
serialized with the exclusive global flock:
pvchange (of orphan), pvresize (of orphan), pvcreate, pvremove,
vgcreate, vgextend, vgremove, vgreduce, vgrename,
vgcfgrestore, vgimportclone, vgmerge, vgsplit
Commands that use a shared flock to read global state (and will
be serialized against the prior list) are those that use
process_each functions that are based on processing a list of
all VG names, or all PVs. The list of all VGs or all PVs is
global state and the shared lock prevents those lists from
changing while the command is processing them.
The ORPHAN lock previously attempted to produce an accurate
listing of orphan PVs, but it was only acquired at the end of
the command during the fake vg_read of the fake orphan vg.
This is not when orphan PVs were determined; they were
determined by elimination beforehand by processing all real
VGs, and subtracting the PVs in the real VGs from the list
of all PVs that had been identified during the initial scan.
This is fixed by holding the single global lock in shared mode
while processing all VGs to determine the list of orphan PVs.
wipe_lv knows it's going to write the device, so it
can open rw from the start. It was opening readonly,
and then dev_write needed to reopen it readwrite.
This reverts 518a8e8cfb
"lvmlockd: activate mirror LVs in shared mode with cmirrord"
because while activating a mirror LV with cmirrord worked,
changes to the active cmirror did not work.
When data are growing, adapt also size of metadata.
As we get way too many reports from users doing huge growths of
data portion while keep metadata small and avoiding using monitoring.
So to enhance the user-experience in case user requests grown of
thin-pool (without passing PV list for growth) - lvm2 will automaticaly
grown also the metadata part of thin-pool (if possible).
Add function for estimation of thin-pool metadata size for given size of
data. Function is using already existing internal API so it can
be reused for resize of thin-pool data.
When lvextend extends an LV that is active with a shared
lock, use this as a signal that other hosts may also have
the LV active, with gfs2 mounted, and should have the LV
refreshed to reflect the new size. Use the libdlmcontrol
run api, which uses dlm_controld/corosync to run an
lvchange --refresh command on other cluster nodes.
Allow using caching with VDO.
User can either cache a single vdopool or
a vdo LV - difference when the caching is put-in depends on a use-case
and it's upto user to decide which kind of speed is expected.
Activation would not be allowed anyway, but we can
check for these cases early and avoid wasted time in
pvscan managing online files an attempting activation.
and "cachepool" to refer to a cache on a cache pool object.
The problem was that the --cachepool option was being used
to refer to both a cache pool object, and to a standard LV
used for caching. This could be somewhat confusing, and it
made it less clear when each kind would be used. By
separating them, it's clear when a cachepool or a cachevol
should be used.
Previously:
- lvm would use the cache pool approach when the user passed
a cache-pool LV to the --cachepool option.
- lvm would use the cache vol approach when the user passed
a standard LV in the --cachepool option.
Now:
- lvm will always use the cache pool approach when the user
uses the --cachepool option.
- lvm will always use the cache vol approach when the user
uses the --cachevol option.
Whenever thin-pool chunk size is unspecified and left for lvm calculation
try to select the size as nearest highest power-of-2 instead of
just being a multiple of 64KiB.
Fixing recent commit 022ebb0cfe
Resize already has size that needs to be counted with,
otherwise upsizing operation could turn into size reduction one.
Now with newer VDO kvdo target we can start to use standard mechanism
to enable resize of VDO volumes.
VDO pool can be grown.
Virtual volume grows on top of VDO pool when is not big enough.
Reduced VDOLV is calling discard for reduced areas - this can
take long time!
TODO: implement some pollable mechanism for out-of-lock TRIM.
When using 'lvcreate -l100%VG' and there is big disproportion between
real available space and requested setting - automatically fallback
to 100%FREE.
Difference can be seen when VG is big and already most space was
allocated, so the requestion 100%VG can end (and by spec for % modifier
it's correct) as LV with size of 1%VG. Usually this is not a big
problem - buit in some cases - like cache-pool allocation, this
can result a big difference for chunksize selection.
With this patch it's more closely match common-sense logic without
the need of reitteration of too big changes in lvm2 core ATM.
TODO: in the future there should be allocator solving all allocations
in a single call.
Drop very old original format of VDO target and focus on V2 version.
So some variables were renamed or replaced.
There is no compatibility preserved (with assumption so far this is
experimental feature and there is no real user).
Note - version currently VDO calls this version 6.2.
This is a followup patch to commit edb72cb70c
to support related lvm2 test suite tests.
A 'global/support_mirrored_mirror_log' bool configuration variable gets
introduced allowing the creation of, or conversion to mirrored 'mirror'
logs if set. The capability to create these in turn allows the rest of
the tests to perform activation of such existing LVs and their conversions
to disk/core 'mirror' logs.
Display a disclaimer warning if enabled that this is not for regular use.
Add definition of the enabled config option to respective test scripts.
Related: rhbz1643562
Scenario: Given an existed LV `lvol0`, I want to create another LV
on the PVs used by `lvol0`.
I use `build_parallel_areas_from_lv()` to obtain the `pv_list` of each segments.
However, the returned `pv_list` is not properly initialized, which causes
segfault in subsequent operations.
There's a small window during creation of a new RaidLV when
rmeta SubLVs are made visible to wipe them in order to prevent
erroneous discovery of stale RAID metadata. In case a crash
prevents the SubLVs from being committed hidden after such
wiping, the RaidLV can still be activated with the SubLVs visible.
During deactivation though, a deadlock occurs because the visible
SubLVs are deactivated before the RaidLV.
The patch adds _check_raid_sublvs to the raid validation in merge.c,
an activation check to activate.c (paranoid, because the merge.c check
will prevent activation in case of visible SubLVs) and shares the
existing wiping function _clear_lvs in raid_manip.c moved to lv_manip.c
and renamed to activate_and_wipe_lvlist to remove code duplication.
Whilst on it, introduce activate_and_wipe_lv to share with
(lvconvert|lvchange).c.
Resolves: rhbz1633167
In RHEL7 we marked mirrored mirror logs as deprecated and
added a related message. This patch prohibits creating new
'mirror' LVs with that log type or converting existing LVs
to have one.
Existing LVs with mirrored mirror log can be activated
and converted to disk/core logs.
Avoid double deprecation message when running lvconvert.
Resolves: rhbz1643562
. When using default settings, this commit should change
nothing. The first PE continues to be placed at 1 MiB
resulting in a metadata area size of 1020 KiB (for
4K page sizes; slightly smaller for larger page sizes.)
. When default_data_alignment is disabled in lvm.conf,
align pe_start at 1 MiB, based on a default metadata area
size that adapts to the page size. Previously, disabling
this option would result in mda_size that was too small
for common use, and produced a 64 KiB aligned pe_start.
. Customized pe_start and mda_size values continue to be
set as before in lvm.conf and command line.
. Remove the configure option for setting default_data_alignment
at build time.
. Improve alignment related option descriptions.
. Add section about alignment to pvcreate man page.
Previously, DEFAULT_PVMETADATASIZE was 255 sectors.
However, the fact that the config setting named
"default_data_alignment" has a default value of 1 (MiB)
meant that DEFAULT_PVMETADATASIZE was having no effect.
The metadata area size is the space between the start of
the metadata area (page size offset from the start of the
device) and the first PE (1 MiB by default due to
default_data_alignment 1.) The result is a 1020 KiB metadata
area on machines with 4KiB page size (1024 KiB - 4 KiB),
and smaller on machines with larger page size.
If default_data_alignment was set to 0 (disabled), then
DEFAULT_PVMETADATASIZE 255 would take effect, and produce a
metadata area that was 188 KiB and pe_start of 192 KiB.
This was too small for common use.
This is fixed by making the default metadata area size a
computed value that matches the value produced by
default_data_alignment.
If a single, standard LV is specified as the cache, use
it directly instead of converting it into a cache-pool
object with two separate LVs (for data and metadata).
With a single LV as the cache, lvm will use blocks at the
beginning for metadata, and the rest for data. Separate
dm linear devices are set up to point at the metadata and
data areas of the LV. These dm devs are given to the
dm-cache target to use.
The single LV cache cannot be resized without recreating it.
If the --poolmetadata option is used to specify an LV for
metadata, then a cache pool will be created (with separate
LVs for data and metadata.)
Usage:
$ lvcreate -n main -L 128M vg /dev/loop0
$ lvcreate -n fast -L 64M vg /dev/loop1
$ lvs -a vg
LV VG Attr LSize Type Devices
main vg -wi-a----- 128.00m linear /dev/loop0(0)
fast vg -wi-a----- 64.00m linear /dev/loop1(0)
$ lvconvert --type cache --cachepool fast vg/main
$ lvs -a vg
LV VG Attr LSize Origin Pool Type Devices
[fast] vg Cwi---C--- 64.00m linear /dev/loop1(0)
main vg Cwi---C--- 128.00m [main_corig] [fast] cache main_corig(0)
[main_corig] vg owi---C--- 128.00m linear /dev/loop0(0)
$ lvchange -ay vg/main
$ dmsetup ls
vg-fast_cdata (253:4)
vg-fast_cmeta (253:5)
vg-main_corig (253:6)
vg-main (253:24)
vg-fast (253:3)
$ dmsetup table
vg-fast_cdata: 0 98304 linear 253:3 32768
vg-fast_cmeta: 0 32768 linear 253:3 0
vg-main_corig: 0 262144 linear 7:0 2048
vg-main: 0 262144 cache 253:5 253:4 253:6 128 2 metadata2 writethrough mq 0
vg-fast: 0 131072 linear 7:1 2048
$ lvchange -an vg/min
$ lvconvert --splitcache vg/main
$ lvs -a vg
LV VG Attr LSize Type Devices
fast vg -wi------- 64.00m linear /dev/loop1(0)
main vg -wi------- 128.00m linear /dev/loop0(0)
lvm uses a bcache block size of 128K. A bcache block
at the end of the metadata area will overlap the PEs
from which LVs are allocated. How much depends on
alignments. When lvm reads and writes one of these
bcache blocks to update VG metadata, it can also be
reading and writing PEs that belong to an LV.
If these overlapping PEs are being written to by the
LV user (e.g. filesystem) at the same time that lvm
is modifying VG metadata in the overlapping bcache
block, then the user's updates to the PEs can be lost.
This patch is a quick hack to prevent lvm from writing
past the end of the metadata area.
This reverts commit 16ae968d24.
We need to come up with a better fix, because we fall short
wiping all known signatures when not using the wipe_lv API.
lvm metadata writes, commits and activations are performed
for (newly) allocated RAID metadata SubLVs to wipe any preexisiting
data thus avoid false raid superblock positives on RaidLV activation.
This process can be interrupted by command or system crashs
thus leaving stale SubLVs in the lvm metadata as a problem.
Because we hold an exclusive lock in this metadata SubLV wiping
process, we can address this problem by avoiding aforementioned
commits/writes/activations altogether wiping the respective first
sector of the first physical extent allocated to any metadata SubLV
directly via the existing dev_set() API.
Succeeds all LVM RAID tests.
Related: rhbz1633167
Allow "lvconvert --type linear RaidLV" on a raid4 LV
providing convenient interim steps to convert to linear.
Add respective new test
lvconvert-raid-takeover-raid4_to_linear.sh
and
lvconvert-raid-takeover-linear_to_raid4.sh
for linear to raid4 once on it.
When converting from striped/raid0/raid0_meta
to raid6 with > 2 stripes, allow possible
direct conversion (to raid6_n_6).
In case of 2 stripes, first convert to raid5_n to restripe
to at least 3 data stripes (the raid6 minimum in lvm2) in
a second conversion before finally converting to raid6_n_6.
As before, raid6_n_6 then can be converted
to any other raid6 layout.
Enhance lvconvert-raid-takeover.sh to test the
2 stripes conversions to raid6.
Resolves: rhbz1624038
"lvconvert --type linear RaidLV" on striped and raid4/5/6/10
have to provide the convenient interim layouts. Fix involves
a cleanup to the convenience type function.
As a result of testing, add missing sync waits to
lvconvert-raid-reshape-linear_to_raid6-single-type.sh.
Resolves: rhbz1447809
Conversion to striped from raid0/raid0_meta is directly possible.
Fix a regression setting superfluous interim raid5_n conversion type
introduced by commit bd7cdd0b09.
Add new test script lvconvert-raid0-striped.sh.
Resolves: rhbz1608067
With improved mirror activation code --splitmirror issue poppedup
since there was missing proper preload code and deactivation
for splitted mirror leg.
Native disk scanning is now both reduced and
async/parallel, which makes it comparable in
performance (and often faster) when compared
to lvm using lvmetad.
Autoactivation now uses local temp files to record
online PVs, and no longer requires lvmetad.
There should be no apparent command-level change
in behavior.
Support vgchange usage with VDO segtype.
Also changing extent size need small update for vdo virtual extent.
TODO: API needs enhancements so it's not about adding ifs() everywhere.
When user create vdo-pool - use different automatic name.
So unlike with traditional LVs using lvol0, lvol1
use vpool0, vpool1...
TODO: apply similar for thin-pool & cache-pool...
When allocating thin-pool with more then 1 device - try to
allocate 'metadataLV' with reuse of log-type allocation for mirror LV.
It should be naturally place on other device then 'dataLV'.
However due to somewhat hard to follow allocation logic code,
it's been rejected allocation in cases where there was not
enough space for data or metadata on single PV, thus to successed,
usage of segments was mandatory.
While user may use:
allocation/thin_pool_metadata_require_separate_pvs=1
to enforce separe meta and data LV - on default settings, this is not
enable thus segment allocation is meant to work.
NOTE:
As already said - the original intention of this whole 'if()' is unclear,
so try to split this test into multiple more simple tests that are more readable.
TODO: more validation.
Allow creation of any virtual segment type with just --virtualsize
specified without any real extent size give.
TODO: likely --type error,zero might be later enhanced to use -V
(along with -L) - but since those targets do not allocate real
space, supporting -V makes sense with them.
It's no longer needed. Clustered VGs are now handled in
the same way as foreign VGs, and as shared VGs that
can't be accessed:
- A command processing all VGs sees a clustered VG,
prints a message ("Skipping clustered VG foo."),
skips it, and does not fail.
- A command where the clustered VG is explicitly
named on the command line, prints a message and fails.
"Cannot access clustered VG foo, see lvmlockd(8)."
The option is listed in the set of ignored options for
the commands that previously accepted it. (Removing it
entirely would cause commands/scripts to fail if they
set it.)
The previous method for forcibly changing a clustered VG
to a local VG involved using -cn and locking_type 0.
Since those options are deprecated, replace it with
the same command used for other forced lock type changes:
vgchange --locktype none --lockopt force.
vgreduce, vgremove and vgcfgrestore were acquiring
the orphan lock in the midst of command processing
instead of at the start of the command. (The orphan
lock moved to being acquired at the start of the
command back when pvcreate/vgcreate/vgextend were
reworked based on pvcreate_each_device.)
vgsplit also needed a small update to avoid reacquiring
a VG lock that it already held (for the new VG name).
A few places were calling a function to check if a
VG lock was held. The only place it was actually
needed is for pvcreate which wants to do its own
locking (and scanning) around process_each_pv.
The locking/scanning exceptions for pvcreate in
process_each_pv/vg_read can be enabled by just passing
a couple of flags instead of checking if the VG is
already locked. This also means that these special
cases won't be enabled unknowingly in other places
where they shouldn't be used.
Different flavors of activate_lv() and lv_is_active()
which are meaningful in a clustered VG can be eliminated
and replaced with whatever that flavor already falls back
to in a local VG.
e.g. lv_is_active_exclusive_locally() is distinct from
lv_is_active() in a clustered VG, but in a local VG they
are equivalent. So, all instances of the variant are
replaced with the basic local equivalent.
For local VGs, the same behavior remains as before.
For shared VGs, lvmlockd was written with the explicit
requirement of local behavior from these functions
(lvmlockd requires locking_type 1), so the behavior
in shared VGs also remains the same.
"lvconvert --type {linear|striped|raid*} ..." on a striped/linear
LV provides convenience interim type to convert to the requested
final layout similar to the given raid* <-> raid* conveninece types.
Whilst on it, add missing raid5_n convenince type from raid5* to raid10.
Resolves: rhbz1439925
Resolves: rhbz1447809
Resolves: rhbz1573255
In this command, lvcreate creates a new LV and then combines
it with an existing cache pool, producing a cache LV. This
command was previously not allowed in in a shared VG.
When the lvmlockd lock is shared, upgrade it to ex
when repair (writing) is needed during vg_read.
Pass the lockd state through additional read-related
functions so the instances of repair scattered through
vg_read can be handled.
(Temporary solution until the ad hoc repairs can be
pulled out of vg_read into a top level, centralized
repair function.)
This minor patch fixes grammar in a few messages which get
printed to users. It also fixes the same grammar mistake in
several comments.
Signed-off-by: Rick Elrod <relrod@redhat.com>
--
The device-mapper directory now holds a copy of libdm source. At
the moment this code is identical to libdm. Over time code will
migrate out to appropriate places (see doc/refactoring.txt).
The libdm directory still exists, and contains the source for the
libdevmapper shared library, which we will continue to ship (though
not neccessarily update).
All code using libdm should now use the version in device-mapper.
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/
Filters are still applied before any device reading or
the label scan, but any filter checks that want to read
the device are skipped and the device is flagged.
After bcache is populated, but before lvm looks for
devices (i.e. before label scan), the filters are
reapplied to the devices that were flagged above.
The filters will then find the data they need in
bcache.
The clvmd saved_vg data is independent from the normal lvm
lvmcache vginfo data, so separate saved_vg from vginfo.
Normal lvm doesn't need to use save_vg at all, and in clvmd,
lvmcache changes on vginfo can be made without worrying
about unwanted effects on saved_vg.
In case "lvconvert -mN RaidLV" was used on a degraded
raid1 LV, success was returned instead of an error.
Provide message to inform about the need to repair first
before changing number of mirrors and exit with error.
Add new lvconvert-m-raid1-degraded.sh test.
Resolves: rhbz1573960
There are likely more bits of code that can be removed,
e.g. lvm1/pool-specific bits of code that were identified
using FMT flags.
The vgconvert command can likely be reduced further.
The lvm1-specific config settings should probably have
some other fields set for proper deprecation.
The mixed up vg repair code in vg_read was trying
to repair a vg when vg_read was called by clvmd.
The clvmd daemon isn't supposed to be repairing
or writing a vg.
(This is a temporary workaround; vg repair will soon
be pulled out of vg_read so it can be called in a
controlled way and consolidated instead of spread
around.)
In some pvmove tests, clvmd uses the new (precommitted)
saved_vg, but then requests the old saved_vg, and
expects that the new saved_vg be returned instead of
the old. So, when returning the new saved_vg, forget
the old one so we don't return it again.
When clvmd does a full label scan just prior to
calling _vg_read(), pass a new flag into _vg_read
to indicate that the normal rescan of VG devs is
not needed.
After reading a VG, stash it in lvmcache as "saved_vg".
Before reading the VG again, try to use the saved_vg.
The saved_vg is dropped on VG lock operations.
For reporting commands (pvs,vgs,lvs,pvdisplay,vgdisplay,lvdisplay)
we do not need to repeat the label scan of devices in vg_read if
they all had matching metadata in the initial label scan. The
data read by label scan can just be reused for the vg_read.
This cuts the amount of device i/o in half, from two reads of
each device to one. We have to be careful to avoid repairing
the VG if we've skipped rescanning. (The VG repair code is very
poor, and will be redone soon.)
Recent changes allow some major simplification of the way
lvmcache works and is used. lvmcache_label_scan is now
called in a controlled fashion at the start of commands,
and not via various unpredictable side effects. Remove
various calls to it from other places. lvmcache_label_scan
should not be called from anywhere during a command, because
it produces an incorrect representation of PVs with no MDAs,
and misclassifies them as orphans. This has been a long
standing problem. The invalid flag and rescanning based on
that is no longer used and removed. The 'force' variation is
no longer needed and removed.
We can't let clvmd keep all scanned devs open,
which prevents them from being removed. So
drop the bcache data (and close fds) affter
doing a label scan.
Also set up bcache before the clvm-specific
vg_read (which needs to rescan the vg's devs
using bcache) and destroy the bcache after.
Drop an extra label scan in the recovery part
of vg_read. This is a temporary improvement
until the pending replacement for the broken
recovery code burried in vg_read.
Create a new dev->bcache_fd that the scanning code owns
and is in charge of opening/closing. This prevents other
parts of lvm code (which do various open/close) from
interfering with the bcache fd. A number of dev_open
and dev_close are removed from the reading path since
the read path now uses the bcache.
With that in place, open(O_EXCL) for pvcreate/pvremove
can then be fixed. That wouldn't work previously because
of other open fds.
The copy of VG metadata stored in lvmcache was not being used
in general. It pretended to be a generic VG metadata cache,
but was not being used except for clvmd activation. There
it was used to avoid reading from disk while devices were
suspended, i.e. in resume.
This removes the code that attempted to make this look
like a generic metadata cache, and replaces with with
something narrowly targetted to what it's actually used for.
This is a way of passing the VG from suspend to resume in
clvmd. Since in the case of clvmd one caller can't simply
pass the same VG to both suspend and resume, suspend needs
to stash the VG somewhere that resume can grab it from.
(resume doesn't want to read it from disk since devices
are suspended.) The lvmcache vginfo struct is used as a
convenient place to stash the VG to pass it from suspend
to resume, even though it isn't related to the lvmcache
or vginfo. These suspended_vg* vginfo fields should
not be used or touched anywhere else, they are only to
be used for passing the VG data from suspend to resume
in clvmd. The VG data being passed between suspend and
resume is never modified, and will only exist in the
brief period between suspend and resume in clvmd.
suspend has both old (current) and new (precommitted)
copies of the VG metadata. It stashes both of these in
the vginfo prior to suspending devices. When vg_commit
is successful, it sets a flag in vginfo as before,
signaling the transition from old to new metadata.
resume grabs the VG stashed by suspend. If the vg_commit
happened, it grabs the new VG, and if the vg_commit didn't
happen it grabs the old VG. The VG is then used to resume
LVs.
This isolates clvmd-specific code and usage from the
normal lvm vg_read code, making the code simpler and
the behavior easier to verify.
Sequence of operations:
- lv_suspend() has both vg_old and vg_new
and stashes a copy of each onto the vginfo:
lvmcache_save_suspended_vg(vg_old);
lvmcache_save_suspended_vg(vg_new);
- vg_commit() happens, which causes all clvmd
instances to call lvmcache_commit_metadata(vg).
A flag is set in the vginfo indicating the
transition from the old to new VG:
vginfo->suspended_vg_committed = 1;
- lv_resume() needs either vg_old or vg_new
to use in resuming LVs. It doesn't want to
read the VG from disk since devices are
suspended, so it gets the VG stashed by
lv_suspend:
vg = lvmcache_get_suspended_vg(vgid);
If the vg_commit did not happen, suspended_vg_committed
will not be set, and in this case, lvmcache_get_suspended_vg()
will return the old VG instead of the new VG, and it will
resume LVs based on the old metadata.
When process_each_pv() calls vg_read() on the orphan VG, the
internal implementation was doing an unnecessary
lvmcache_label_scan() and two unnecessary label_read() calls
on each orphan. Some of those unnecessary label scans/reads
would sometimes be skipped due to caching, but the code was
always doing at least one unnecessary read on each orphan.
The common format_text case was also unecessarily calling into
the format-specific pv_read() function which actually did nothing.
By analyzing each case in which vg_read() was being called on
the orphan VG, we can say that all of the label scans/reads
in vg_read_orphans are unnecessary:
1. reporting commands: the information saved in lvmcache by
the original label scan can be reported. There is no advantage
to repeating the label scan on the orphans a second time before
reporting it.
2. pvcreate/vgcreate/vgextend: these all share a common
implementation in pvcreate_each_device(). That function
already rescans labels after acquiring the orphan VG lock,
which ensures that the command is using valid lvmcache
information.
Move the location of scans to make it clearer and avoid
unnecessary repeated scanning. There should be one scan
at the start of a command which is then used through the
rest of command processing.
Previously, the initial label scan was called as a side effect
from various utility functions. This would lead to it being called
unnecessarily. It is an expensive operation, and should only be
called when necessary. Also, this is a primary step in the
function of the command, and as such it should be called prominently
at the top level of command processing, not as a hidden side effect
of a utility function. lvm knows exactly where and when the
label scan needs to be done. Because of this, move the label scan
calls from the internal functions to the top level of processing.
Other specific instances of lvmcache_label_scan() are still called
unnecessarily or unclearly by specific commands that do not use
the common process_each functions. These will be improved in
future commits.
During the processing phase, rescanning labels for devices in a VG
needs to be done after the VG lock is acquired in case things have
changed since the initial label scan. This was being done by way
of rescanning devices that had the INVALID flag set in lvmcache.
This usually approximated the right set of devices, but it was not
exact, and obfuscated the real requirement. Correct this by using
a new function that rescans the devices in the VG:
lvmcache_label_rescan_vg().
Apart from being inexact, the rescanning was extremely well hidden.
_vg_read() would call ->create_instance(), _text_create_text_instance(),
_create_vg_text_instance() which would call lvmcache_label_scan()
which would call _scan_invalid() which repeats the label scan on
devices flagged INVALID. lvmcache_label_rescan_vg() is now called
prominently by _vg_read() directly.
To do label scanning, lvm code calls lvmcache_label_scan().
Change lvmcache_label_scan() to use the new label_scan()
based on bcache.
Also add lvmcache_label_rescan_vg() which calls the new
label_scan_devs() which does label scanning on only the
specified devices. This is for a subsequent commit and
is not yet used.
New label_scan function populates bcache for each device
on the system.
The two read paths are updated to get data from bcache.
The bcache is not yet used for writing. bcache blocks
for a device are invalidated when the device is written.
