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A cachevol can be forcibly detached when it's missing devices.
Also allow this if it's damaged/invalid and unrepairable.
This would be needed to recover data from the origin LV after
a cachevol is lost or damaged beyond repair.
In cases where lvconvert does not detect a fs block size on the
device, it falls back to choosing a writecache block size based
on the device's LBS and PBS (tries to match those.)
If the user specifies a writecache block size on the command
line (--cachesettings block_size=4096|512), lvconvert currently
fails and reports an error if the user-specified value does not
match the value lvconvert would have chosen based on LBS and PBS.
The purpose of allowing a user-specified value on the command line
is to override what lvconvert would otherwise do, so change this
to just print a warning that the user value does not match the
value that would be chosen based on the LBS/PBS, and then take
the user-specified value as the writecache block size.
Use update_pool_metadata_min_max() which is shared with
thin-pool metadata min-max updating.
Gives improved messages when converting volumes to metadata.
Initial support for thin-pool used slightly smaller max size 15.81GiB
for thin-pool metadata. However the real limit later settled at 15.88GiB
(difference is ~64MiB - 16448 4K blocks).
lvm2 could not simply increase the size as it has been using hard cropping
of the loaded metadata device to avoid warnings printing warning of kernel
when the size was bigger (i.e. due to bigger extent_size).
This patch adds the new lvm.conf configurable setting:
allocation/thin_pool_crop_metadata
which defaults to 0 -> no crop of metadata beyond 15.81GiB.
Only user with these sizes of metadata will be affected.
Without cropping lvm2 now limits metadata allocation size to 15.88GiB.
Any space beyond is currently not used by thin-pool target.
Even if i.e. bigger LV is used for metadata via lvconvert,
or allocated bigger because of to large extent size.
With cropping enabled (=1) lvm2 preserves the old limitation
15.81GiB and should allow to work in the evironement with
older lvm2 tools (i.e. older distribution).
Thin-pool metadata with size bigger then 15.81G is now using CROP_METADATA
flag within lvm2 metadata, so older lvm2 recognizes an
incompatible thin-pool and cannot activate such pool!
Users should use uncropped version as it is not suffering
from various issues between thin_repair results and allocated
metadata LV as thin_repair limit is 15.88GiB
Users should use cropping only when really needed!
Patch also better handles resize of thin-pool metadata and prevents resize
beoyond usable size 15.88GiB. Resize beyond 15.81GiB automatically
switches pool to no-crop version. Even with existing bigger thin-pool
metadata command 'lvextend -l+1 vg/pool_tmeta' does the change.
Patch gives better controls 'coverted' metadata LV and
reports less confusing message during conversion.
Patch set also moves the code for updating min/max into pool_manip.c
for better sharing with cache_pool code.
When detaching writecache, make the first stage send a message
to dm-writecache to set the cleaner option. This is instead of
reloading the dm table with the cleaner option set. Reloading
the table causes udev to process/probe the dm dev, which gets
stalled because of the writeback activity, and the stalled udev
in turn stalls the lvconvert command when it tries to sync with
udev events.
When getting writecache status we do not need to get
open_count or read_head info, which can cause extra steps.
Read buffersize - 1 so the last byte is always 0.
Simplify init of 0 buffers.
Check snprintf result for error and report internal error as it could
happen only via bad compile parameters.
Fix the two-step writecache detach in commit c32d7fed4f.
In the case of uncache, the cachevol is removed after
detaching the writecache. When the detach is finished
in the second step, the remove must wait until then.
filters needing io weren't being run because bcache
wasn't set up. Read the first 4k of the device
before doing filtering or reading ondisk structs to
reduce reads.
It's possible for a machine with a non-4k page size
to create a PV with an mda_header at an offset other
than 4k. Fix pvck --dump to work with these other
mda offsets. pvck --repair will write a new first
mda at 4096 but lvm with other page sizes will work
with this.
The args for pvcreate/pvremove (and vgcreate/vgextend
when applicable) were not efficiently opened, scanned,
and filtered. This change reorganizes the opening
and filtering in the following steps:
- label scan and filter all devs
. open ro
. standard label scan at the start of command
- label scan and filter dev args
. open ro
. uses full md component check
. typically the first scan and filter of pvcreate devs
- close and reopen dev args
. open rw and excl
- repeat label scan and filter dev args
. using reopened rw excl fd
- wipe and write new headers
. using reopened rw excl fd
Since 'kilobytes' could be seen in 2 way - SI as '1000',
while all programmers sees it as '1024' - switch to
commonly acceptted KiB, MiB....
Resolves RHBZ 1496255.
Restructure the pvscan code, and add new temporary files
that list pvids in a VG, used for processing PVs that
have no metadata.
The new temp files, in /run/lvm/pvs_lookup/<vgname>, allow a
proper pvscan --cache to be done on PVs that have no metadata.
pvscan --cache <dev> is only supposed to read <dev>, but when
<dev> has no metadata, this had not been possible. The
command had to fall back to scanning all devices to read all
VG metadata to get the list of all PVIDs needed to check for
a complete VG. Now, the temp file can be used in place of
reading metadata from all PVs on the system.
cmd context has 'threaded' value that used be set
by clvmd - and allowed proper memory locking management.
Reuse same bit for dmeventd.
Since dmeventd is using 300KiB stack per thread,
we will ignore any user settings for allocation/reserved_stack
until some better solution is find.
This avoids crashing of dmevend when user changes this value
and because in most cases lvm2 should work ok with 64K stack
size, this change should not cause any problems.
When detaching a writecache, use the cleaner setting
by default to writeback data prior to suspending the
lv to detach the writecache. This avoids potentially
blocking for a long period with the device suspended.
Detaching a writecache first sets the cleaner option, waits
for a short period of time (less than a second), and checks
if the writecache has quickly become clean. If so, the
writecache is detached immediately. This optimizes the case
where little writeback is needed.
If the writecache does not quickly become clean, then the
detach command leaves the writecache attached with the
cleaner option set. This leaves the LV in the same state
as if the user had set the cleaner option directly with
lvchange --cachesettings cleaner=1 LV.
After leaving the LV with the cleaner option set, the
detach command will wait and watch the writeback progress,
and will finally detach the writecache when the writeback
is finished. The detach command does not need to wait
during the writeback phase, and can be canceled, in which
case the LV will remain with the writecache attached and
the cleaner option set. When the user runs the detach
command again it will complete the detach.
To detach a writecache directly, without using the cleaner
step (which has been the approach previously), add the
option --cachesettings cleaner=0 to the detach command.
Reorganize checking the device args for pvcreate/pvremove
to prepare for future changes. There should be no change
in behavior. Stop the inverted use of process_each_pv,
which pulled in a lot of unnecessary processing, and call
the check functions on each device directly.
LVM2 is distributed under GPLv2 only. The readline library changed its
license long ago to GPLv3. Given that those licenses are incompatible
and you follow the FSF in their interpretation that dynamically linking
creates a derivative work, distributing LVM2 linked against a current
readline version might be legally problematic.
Add support for the BSD licensed editline library as an alternative for
readline.
Link: https://thrysoee.dk/editline
There's a bug when lvpoll attempts to write new hints,
related to the fact that lvpoll does not follow the same
scanning process as standard commands.
Fix by disabling the use of hints in lvpoll. We may want
to renable hints in lvpoll in a way that they can be used,
if valid, but not updated if they don't exist or are invalid.
Add a "device index" (di) for each device, and use this
in the bcache api to the rest of lvm. This replaces the
file descriptor (fd) in the api. The rest of lvm uses
new functions bcache_set_fd(), bcache_clear_fd(), and
bcache_change_fd() to control which fd bcache uses for
io to a particular device.
. lvm opens a dev and gets and fd.
fd = open(dev);
. lvm passes fd to the bcache layer and gets a di
to use in the bcache api for the dev.
di = bcache_set_fd(fd);
. lvm uses bcache functions, passing di for the dev.
bcache_write_bytes(di, ...), etc.
. bcache translates di to fd to do io.
. lvm closes the device and clears the di/fd bcache state.
close(fd);
bcache_clear_fd(di);
In the bcache layer, a di-to-fd translation table
(int *_fd_table) is added. When bcache needs to
perform io on a di, it uses _fd_table[di].
In the following commit, lvm will make use of the new
bcache_change_fd() function to change the fd that
bcache uses for the dev, without dropping cached blocks.
Cow may not be a COW type, the return value of origin_from_cow(cow) may be NULL.
Reported-by: Wu Guanghao <wuguanghao3@huawei.com>
Reported-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Cow may not be a snapshot type, the return value of origin_from_cow(cow) may be NULL
Signed-off-by: Wu Guanghao <wuguanghao3@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
LV may not be a snapshot type, the return value of find_snapshot(lv) may be NULL.
Here, we will call stack if LV is not a snapshot type.
Signed-off-by: Wu Guanghao <wuguanghao3@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
The return value of top_level_lv_name() may be NULL, so we should
check return value of top_level_lv_name before calling
strcmp(lv->name, top_level_lv_name(vg, lv_name)).
Signed-off-by: Wu Guanghao <wuguanghao3@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Use '0' for error and '1' as success.
Also drop INTERNAL_ERROR from path - as this error
is ATM used for invalid devices.
(i.e. test lvconvert-raid1-split-trackchanges.sh)
Since we declare dev_name in lib/device/device.h
and pvs in commands.h
rename local dev_name to device_name
and pvs to pvs_list to prevent shadowing warning.
m
Switch remaining zero sized struct to flexible arrays to be C99
complient.
These simple rules should apply:
- The incomplete array type must be the last element within the structure.
- There cannot be an array of structures that contain a flexible array member.
- Structures that contain a flexible array member cannot be used as a member of another structure.
- The structure must contain at least one named member in addition to the flexible array member.
Although some of the code pieces should be still improved.
Allow the optional '--type raid1' to be included in the lvconvert
command when adding or removing raid images with integrity.
It does not change the meaning of the command (specifying a type
that matches the current type is redundant but generally allowed.)
When converting volume to pool LV use also wiping of other signatures.
For writecache & pool conversion support --yet and --force
to bypass prompting for signature wiping.
For writecache drop unneded zero_sectors.
Note: currently we have lvconvert doing convertion and prompting
for confirmation of conversion - and then again wipe_lv() prompts
for removing i.e. filesystem signature - we should unify this
prompting into 1 message - althought the 'filesystem' discovery
needs active volume - while the 1st. conversion prompt can
work without active converted volume.
To create a new cache or writecache LV with a single command:
lvcreate --type cache|writecache
-n Name -L Size --cachedevice PVfast VG [PVslow ...]
- A new main linear|striped LV is created as usual, using the
specified -n Name and -L Size, and using the optionally
specified PVslow devices.
- Then, a new cachevol LV is created internally, using PVfast
specified by the cachedevice option.
- Then, the cachevol is attached to the main LV, converting the
main LV to type cache|writecache.
Include --cachesize Size to specify the size of cache|writecache
to create from the specified --cachedevice PVs, otherwise the
entire cachedevice PV is used. The --cachedevice option can be
repeated to create the cache from multiple devices, or the
cachedevice option can contain a tag name specifying a set of PVs
to allocate the cache from.
To create a new cache or writecache LV with a single command
using an existing cachevol LV:
lvcreate --type cache|writecache
-n Name -L Size --cachevol LVfast VG [PVslow ...]
- A new main linear|striped LV is created as usual, using the
specified -n Name and -L Size, and using the optionally
specified PVslow devices.
- Then, the cachevol LVfast is attached to the main LV, converting
the main LV to type cache|writecache.
In cases where more advanced types (for the main LV or cachevol LV)
are needed, they should be created independently and then combined
with lvconvert.
Example
-------
user creates a new VG with one slow device and one fast device:
$ vgcreate vg /dev/slow1 /dev/fast1
user creates a new 8G main LV on /dev/slow1 that uses all of
/dev/fast1 as a writecache:
$ lvcreate --type writecache --cachedevice /dev/fast1
-n main -L 8G vg /dev/slow1
Example
-------
user creates a new VG with two slow devs and two fast devs:
$ vgcreate vg /dev/slow1 /dev/slow2 /dev/fast1 /dev/fast2
user creates a new 8G main LV on /dev/slow1 and /dev/slow2
that uses all of /dev/fast1 and /dev/fast2 as a writecache:
$ lvcreate --type writecache --cachedevice /dev/fast1 --cachedevice /dev/fast2
-n main -L 8G vg /dev/slow1 /dev/slow2
Example
-------
A user has several slow devices and several fast devices in their VG,
the slow devs have tag @slow, the fast devs have tag @fast.
user creates a new 8G main LV on the slow devs with a
2G writecache on the fast devs:
$ lvcreate --type writecache -n main -L 8G
--cachedevice @fast --cachesize 2G vg @slow
To add a cache or writecache to a main LV with a single command:
lvconvert --type cache|writecache --cachedevice /dev/ssd vg/main
A cachevol LV will be allocated from the specified cache device,
then attached to the main LV. Include --cachesize to specify the
size of cachevol to create, otherwise the entire cachedevice is
used. The cachedevice option can be repeated to create a cachevol
from multiple devices.
Example
-------
A user has an existing main LV that they want to speed up
using a new ssd.
user adds the new ssd to the VG:
$ vgextend vg /dev/ssd
user attaches the new ssd their main LV:
$ lvconvert --type writecache --cachedevice /dev/ssd vg/main
Example
-------
A user has two existing main LVs that they want to speed up
with a new ssd.
user adds the new 16G ssd to the VG:
$ vgextend vg /dev/ssd
user attaches some of the new ssd to the first main LV,
using half of the space:
$ lvconvert --type writecache --cachedevice /dev/ssd
--cachesize 8G vg/main1
user attaches some of the new ssd to the second main LV,
using the other half of the space:
$ lvconvert --type writecache --cachedevice /dev/ssd
--cachesize 8G vg/main2
Example
-------
A user has an existing main LV that they want to speed up using
two new ssds.
user adds the new two ssds the VG:
$ vgextend vg /dev/ssd1
$ vgextend vg /dev/ssd2
user attaches both ssds their main LV:
$ lvconvert --type writecache
--cachedevice /dev/ssd1 --cachedevice /dev/ssd2 vg/main
Use libblkid to detect sector/block size of the fs on the LV.
Use this to choose a compatible writecache block size.
Enable attaching writecache to an active LV.
When lvconvert is used to remove raid images, we can
skip calling lv_add_integrity_to_raid(), which finds
nothing to do, but the the blocksize validation would
be called unnecessarily and trigger spurious errors.
pvck --dump headers reads the metadata text area
to compute the text metadata checksum to compare
with the mda_header checksum.
The new header_only will skip reading the metadata
text and not validate the mda_header checksum.
dm-integrity stores checksums of the data written to an
LV, and returns an error if data read from the LV does
not match the previously saved checksum. When used on
raid images, dm-raid will correct the error by reading
the block from another image, and the device user sees
no error. The integrity metadata (checksums) are stored
on an internal LV allocated by lvm for each linear image.
The internal LV is allocated on the same PV as the image.
Create a raid LV with an integrity layer over each
raid image (for raid levels 1,4,5,6,10):
lvcreate --type raidN --raidintegrity y [options]
Add an integrity layer to images of an existing raid LV:
lvconvert --raidintegrity y LV
Remove the integrity layer from images of a raid LV:
lvconvert --raidintegrity n LV
Settings
Use --raidintegritymode journal|bitmap (journal is default)
to configure the method used by dm-integrity to ensure
crash consistency.
Initialization
When integrity is added to an LV, the kernel needs to
initialize the integrity metadata/checksums for all blocks
in the LV. The data corruption checking performed by
dm-integrity will only operate on areas of the LV that
are already initialized. The progress of integrity
initialization is reported by the "syncpercent" LV
reporting field (and under the Cpy%Sync lvs column.)
Example: create a raid1 LV with integrity:
$ lvcreate --type raid1 -m1 --raidintegrity y -n rr -L1G foo
Creating integrity metadata LV rr_rimage_0_imeta with size 12.00 MiB.
Logical volume "rr_rimage_0_imeta" created.
Creating integrity metadata LV rr_rimage_1_imeta with size 12.00 MiB.
Logical volume "rr_rimage_1_imeta" created.
Logical volume "rr" created.
$ lvs -a foo
LV VG Attr LSize Origin Cpy%Sync
rr foo rwi-a-r--- 1.00g 4.93
[rr_rimage_0] foo gwi-aor--- 1.00g [rr_rimage_0_iorig] 41.02
[rr_rimage_0_imeta] foo ewi-ao---- 12.00m
[rr_rimage_0_iorig] foo -wi-ao---- 1.00g
[rr_rimage_1] foo gwi-aor--- 1.00g [rr_rimage_1_iorig] 39.45
[rr_rimage_1_imeta] foo ewi-ao---- 12.00m
[rr_rimage_1_iorig] foo -wi-ao---- 1.00g
[rr_rmeta_0] foo ewi-aor--- 4.00m
[rr_rmeta_1] foo ewi-aor--- 4.00m
lvm2 supports thin-pool to be later used by other tools doing
virtual volumes themself (i.e. docker) - in this case we
shall not validate transaction Id - is this is used by
other tools and lvm2 keeps value 0 - so the transationId
validation need to be skipped in this case.
Prevent attaching writecache to an active LV until
we can determine the block size of the fs on the LV,
and use that to enforce an appropriate writecache
block size. Changing the block size under a mounted
fs can cause panic/corruption.
Currently the error messages are not clear. This very easy to
guide user to execute "--removemissing --force", it is dangerous
and will make the LVs to be destroied.
Signed-off-by: Zhao Heming <heming.zhao@suse.com>
Since VDO is also pool, the old if() case missed to know about this,
and executed unnecesserily initialization of cache pool variables.
This was usually harmless when using 'smaller' sizes of VDO pools,
but for big VDO pool size, we were reporting senseless messages
about big cache chunk sizes.
To write a new/repaired pv_header and label_header:
pvck --repairtype pv_header --file <file> <device>
This uses the metadata input file to find the PV UUID,
device size, and data offset.
To write new/repaired metadata text and mda_header:
pvck --repairtype metadata --file <file> <device>
This requires a good pv_header which points to one or two
metadata areas. Any metadata areas referenced by the
pv_header are updated with the specified metadata and
a new mda_header. "--settings mda_num=1|2" can be used
to select one mda to repair.
To combine all header and metadata repairs:
pvck --repair --file <file> <device>
It's best to use a raw metadata file as input, that was
extracted from another PV in the same VG (or from another
metadata area on the same PV.) pvck will also accept a
metadata backup file, but that will produce metadata that
is not identical to other metadata copies on other PVs
and other areas. So, when using a backup file, consider
using it to update metadata on all PVs/areas.
To get a raw metadata file to use for the repair, see
pvck --dump metadata|metadata_search.
List all instances of metadata from the metadata area:
pvck --dump metadata_search <device>
Save one instance of metadata at the given offset to
the specified file (this file can be used for repair):
pvck --dump metadata_search --file <file>
--settings "metadata_offset=<off>" <device>
using --settings:
mda_offset=<offset> mda_size=<size> can be used
in place of the offset/size that normally come
from headers.
metadata_offset=<offset> prints/saves one instance
of metadata text at the given offset, in
metadata_all or metadata_search.
This reverts commit 7474440d3b.
lvs can use the scanning optimization again since it has
been changed in:
"scanning: optimize by checking text offset and checksum"
The kernel MD runtime requires region size to be larger than stripe size
on striped raid layouts, thus the dm-raid target's constructor rejects
such request.
This causes e.g. an 'lvcreate --type raid10 -i3 -I4096 -R2048 -n lv vg' to fail.
Avoid failing late in the kernel by enforcing region size to be
larger or equal to stripe size.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1698225
When pvcreate/pvremove prompt the user, they first release
the global lock, then acquire it again after the prompt,
to avoid blocking other commands while waiting for a user
response. This release/reacquire changes the locking
order with respect to the hints flock (and potentially other
locks). So, to avoid deadlock, use a nonblocking request
when reacquiring the global lock.
The scanning optimization can produce warnings from
'lvs' when run concurrently with commands modifying LVs,
so disable the optimization until it can be improved.
Without the scanning optimization, lvs will always
read all PVs twice:
1. read metadata from all PVs, saving it in memory
2. for each VG
3. lock VG
4. reread metadata from all PVs in VG, replacing metadata
saved from step 1
5. run command on VG
6. unlock VG
The optimization would usually cause step 4 to be skipped,
and PVs would be read only once.
Running the command in step 5 using metadata that was not
read under the VG lock is usually fine, except for the
fact that lvs attempts to validate the metadata by comparing
it to current dm state. If other commands are modifying dm
state while lvs is running, lvs may see differences between
metadata from step 1 and dm state checked during step 5,
and print warnings.
(A better fix may be to detect the concurrent change and
fall back to rereading metadata in step 4 only when needed.)
Since we check for NULL pointers earlier we need
to be consistent across function - since the NULL
would applies across whole function.
When dropping 'mda' check - we are actually
already dereferencing it before - so it can't
be NULL at that places (and it's validated
before entering _read_mda_header_and_metadata).
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 a user includes "--type foo" in a command, only
look at command definitions with matching type, as
opposed to using matching/mismatching --type as a
vote for/against a given command def. This means a
command with --type foo will prioritize a command def
with --type foo over other command defs that have
more matching options but an unmatching type. This
makes it more likely that a closely matching command
def will be recommended.
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.
Improve the implementation of extracting all text metadata
copies from the metadata area. Use this for the existing
metadata_all dump option.
Add a new metadata_search dump option which does not use
lvm headers to find metadata, but looks in standard
locations. This is useful if headers are damaged and
can't be used to locate metadata.
Adding '-v' to metadata_all or metadata_search will add
the description and creation_time to the printed list of
metadata instances that are found.
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).
When an LV is used as a writecache cachevol, give
it the LV name a _cvol suffix. Remove the suffix
when the cachevol is detached, restoring the
original LV name.
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.
Instead of using 'noflush' option, switch cache_mode into WRITETHROUGH
which does not require flushing, when user confirmed he does not
want flushing for WRITEBACK (because of (partially) missing caching PV)
For wiping we activate and clear 'regular' devices,
since in case of whole process interuption (i.e. kill -9)
we leave metadata & DM table and workable state all the time.
vgck --updatemetadata would write the same correct
metadata to good mdas, and then to bad mdas, but the
sequence of vg_write/vg_commit calls betwen good and
bad mdas could cause a different description field to
be generated for good/bad mdas. (The description field
describing the command was recently included in the
ondisk copy of the metadata text.)
When the PV device names in the VG metadata do not match the
current PV device names seen on the system, do not use the
optimized activation function (that avoids extra device scanning.)
When the device names do not match, it's a clue that there could
be duplicate PVs, in which case we want to scan all devicess to
find any duplicates and stop the activation if found.
This does not prevent autoactivating a VG from the incorrect
duplicate PV, because the incorrect duplicate may appear by itself
first. At that point its duplicate PV does not exist to be seen.
(A future enhancement could use the WWID to strengthen this
detection.)
- 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 pvscan is used to activate a VG via an
asynchronous service (i.e. lvm2-pvscan), there
is no requirement that the command wait for
udev to create device nodes before returning.
It's possible that waiting for udev is slow
enough to cause the service running the command
to time out. So, allow the --noudevsync option
to be given to pvscan to skip waiting for udev.
(This commit is not changing the lvm2-pvscan
service itself to use --noudevsync.)
Still unknown is whether there are any complex
LV activation cases in which lvm itself requires
access to a device node, in which case the udev
wait could be needed by lvm itself.
(When running an activation command directly
from the command line, it's generally expected
that the activated LVs are ready to use when
the command is finished, so lvm waits for
udev to finish creating the dev nodes.)
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.
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...
Between 'resume' and 'remove' we need to wait for udev to synchronize,
otherwise udev may 'skip' resume event processing if the udev node
is already gone.
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.
An active md device with an end superblock causes lvm to
enable full md component detection. This was being done
within the filter loop instead of before, so the full
filtering of some devs could be missed.
Also incorporate the recently added config setting that
controls the md component detection.
Fix commit 7836e7aa1c
"pvscan: ignore device with incorrect size"
which caused pvscan to not consider a PV online (for purposes
of event based activation) if the PV and device sizes differed.
This helped to avoid mistaking MD components for PVs, and is
replaced by triggering an md component check when PV and device
sizes differ (which happens in set_pv_device).
This allows the creation of a striped mirror leg(s) during upconvert
by adding lvconvert command line options --stripes/--stripesize
for 'mirror' to tools/command-lines.in.
In case multiple mirror legs are being added, all will have the
same requested striped layout.
Resolves: rhbz1720705
The cache repair utility does not yet work with a cachevol
(where metadata and data exist on the same LV.) So, warn
and prompt if writeback is specified with a cachevol.
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.
When monitoring, skip exported VGs without causing a command
failure.
The lvm2-monitor service runs 'vgchange --monitor y', so
any exported VG on the system would cause the service to
fail.
The man page generation for pvchange/lvchange/vgchange was
incorrect (leaving out some option listings) as a result of
commit e225bf5 "fix command definition for pvchange -a"
The -a was being included in the set of "one or more"
options instead of an actual required option. Even
though the cmd def was not implementing the restrictions
correctly, the command internally was.
Adjust the cmd def code which did not support a command
with some real required options and a set of "one or more"
options.
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.
These two flags may be not reset at the end of
the command when the unlock is implicit, which
is a problem if the cmd struct is reused.
Clear the flags in the general fin_locking.
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
If udev info is missing for a device, (which would indicate
if it's an MD component), then do an end-of-device read to
check if a PV is an MD component. (This is skipped when
using hints since we already know devs in hints are good.)
A new config setting md_component_checks can be used to
disable the additional end-of-device MD checks, or to
always enable end-of-device MD checks.
When both hints and udev info are disabled/unavailable,
the end of PVs will now be scanned by default. If md
devices with end-of-device superblocks are not being
used, the extra I/O overhead can be avoided by setting
md_component_checks="start".
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.
Add 'pvck --dump headers' to print all the
lvm ondisk structs. Also checks the values
and prints any problems.
The previous dump metadata is also converted to
use these same routines, which do not depend on lvm
fully scanning/reading/processing the headers and
metadata on disk. This makes it useful to get data in
cases where there is corruption that would otherwise
prevent the normal functions from working.
The new command 'pvck --dump metadata PV' will extract
the current version of VG metadata from a PV for testing
and debugging. --dump metadata_area extracts the entire
text metadata area.
commit aa75b31db5
"pvscan: handle case of scanning PV without metadata last"
failed to recognize that an arg may be null in the case of
'pvscan --cache' (without -aay) which does not keep track
of complete VGs because it does not need to activate them.
The scanning rework missed removing this instance of label scan.
It's no longer needed because of the way that label scan is always
run once from the start of the command. This unnecessary scan
would be triggered by running 'pvs @tag'.
and don't call it from inside pvcreate_each_device.
This avoids having to repeat it for users of
pvcreate_each_device (pvcreate/pvremove/vgcreate/vgextend.)
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.
Handle the case where pvscan --cache -aay (with no dev args)
gets to the final PV, completing the VG, but that final PV does not
have VG metadata. In this case, we need to use VG metadata from a
previously scanned PV in the same VG, which we saved for this
possibility. Using this saved metadata, we can find which VG
this PVID belongs to, and then check if that VG is now complete,
and if so add the VG name to the list of complete VGs to be
autoactivated.
If a device looks like a PV, but its size does not
match the PV size in the metadata, then skip it for
purposes of autoactivation. It's probably not wrong
device for the PV.
In the past, the first 'pvscan --cache -aay dev' command
to run on the system would initialize the pvs_online dir
by scanning all devs and creating online files for all pvs
it found, and then autoactivating the VG (if complete) for
the named dev. The idea was that the system may not have
been able to run pvscan commands for early devices, so the
first pvscan to run would need to "make up" for any devices
that had appeared previously, which the system was unable to
scan. The problem or idea of making up for missed scans is
historical and should no longer be needed, so remove this
special init case.
When pvscan is run for the initialization case (the first
pvscan run on the system), it scans all devs and creates
online files for all PVs it finds. Previously it would
then autoactivate every complete VG, but change this to
only autoactive the (complete) VG corresponding to the
named device arg(s).
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.
Fix to previous commit
"pvscan: ignore online for shared and foreign PVs"
which was incorrectly considering a PV foreign if its
VG had no system ID when the host did have a system ID.
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.
Without this, the output from different commands in a single
log file could not be separated.
Change the default "indent" setting to 0 so that the default
debug output does not include variable spaces in the middle
of debug lines.
When a VG has multiple PVs, and all those PVs come online
at the same time, concurrent pvscans for each PV will all
create the individual pvid files, and all will often see
the VG is now complete. This causes each of the pvscan
commands to think it should activate the VG, so there
are multiple activations of the same VG. The vg lock
serializes them, and only the first pvscan actually does
the activation, but there is still a lot of extra overhead
and time used by the other pvscans that attempt to
activate the already active VG. This can lead to a backlog
of pvscans and timeouts.
To fix this, this adds a new /run/lvm/vgs_online/ dir that
works like the existing /run/lvm/pvs_online/ dir. Each pvscan
that wants to activate a VG will first try to exlusively create
the file vgs_online/<vgname>. Only the first pvscan will
succeed, and that one will do the VG activation. The other
pvscans will find the vgname file exists and will not do the
activation step.
When a PV goes offline, the vgs_online file for the corresponding
VG is removed. This allows the VG to be autoactivated again
when the PV comes online again. This requires that the vgname be
stored in the pvid files.
Use a file lock to ensure that only one pvscan will do
initialization of pvs_online, otherwise multiple concurrent
pvscans may all see an empty pvs_online directory and
do initialization.
The pvscan that is doing initialization should also only
attempt to activate complete VGs.
When aay was included in the pvscan --cache command,
the activation part was complaining about the unusual
state of the hint file since it had been recreated
just prior.
Just like we support for thin-pool syntax:
lvcreate --thinpool new_tpoolname -L Size vg
add same support logic with for vdo-poo:
lvcreate --vdopool new_vpoolname -L Size vg
Also move description of syntax bellow thin-pool, so it's
correctly ordered in generated man page.
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.
An idea from Zdenek for better ensuring valid hints by invalidating
them when pvscan --cache <device> sees a new PV, which is a case
where we know that hints should be invalidated. This is triggered
from systemd/udev logic, and there may be some cases where it would
invalidate hints that the existing methods wouldn't detect.
If there are two independent scripts doing:
vgchange --lockstart vg
lvchange -ay vg/lv
The first vgchange to do the lockstart will wait for
the lockstart to complete before returning.
The second vgchange to do the lockstart will see that
the start is already in progress (from the first) and
will do nothing. This means the second does not wait
for any lockstart to complete, and moves on to the
lvchange which may find the lockspace still starting
and fail.
To fix this, make the vgchange lockstart command
wait for any lockstart's in progress to complete.
Save the list of PVs in /run/lvm/hints. These hints
are used to reduce scanning in a number of commands
to only the PVs on the system, or only the PVs in a
requested VG (rather than all devices on the system.)
When initializing an LV to hold the writecache, use wipe_lv()
which looks for specific signatures on the LV.
Wiping signatures is not necessary, but printing a warning
that names a specific signature (in addition to the existing
generic warning/confirmation) may help if a user accidentally
specifies the wrong LV which contains something important.
