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Apply the same idea as vg_update.
Before doing the VG remove on disk, invalidate
the VG in lvmetad. After the VG is removed,
remove the VG in lvmetad. If the command fails
after removing the VG on disk, but before removing
the VG metadata from lvmetad, then a subsequent
command will see the INVALID flag and not use the
stale metadata from lvmetad.
Previously, a command sent lvmetad new VG metadata in vg_commit().
In vg_commit(), devices are suspended, so any memory allocation
done by the command while sending to lvmetad, or by lvmetad while
updating its cache could deadlock if memory reclaim was triggered.
Now lvmetad is updated in unlock_vg(), after devices are resumed.
The new method for updating VG metadata in lvmetad is in two phases:
1. In vg_write(), before devices are suspended, the command sends
lvmetad a short message ("set_vg_info") telling it what the new
VG seqno will be. lvmetad sees that the seqno is newer than
the seqno of its cached VG, so it sets the INVALID flag for the
cached VG. If sending the message to lvmetad fails, the command
fails before the metadata is committed and the change is not made.
If sending the message succeeds, vg_commit() is called.
2. In unlock_vg(), after devices are resumed, the command sends
lvmetad the standard vg_update message with the new metadata.
lvmetad sees that the seqno in the new metadata matches the
seqno it saved from set_vg_info, and knows it has the latest
copy, so it clears the INVALID flag for the cached VG.
If a command fails between 1 and 2 (after committing the VG on disk,
but before sending lvmetad the new metadata), the cached VG retains
the INVALID flag in lvmetad. A subsequent command will read the
cached VG from lvmetad, see the INVALID flag, ignore the cached
copy, read the VG from disk instead, update the lvmetad copy
with the latest copy from disk, (this clears the INVALID flag
in lvmetad), and use the correct VG metadata for the command.
(This INVALID mechanism already existed for use by lvmlockd.)
Previously, vgcfgrestore would attempt to vg_remove the
existing VG from lvmetad and then vg_update to add the
restored VG. But, if there was a failure in the command
or with vg_update, the lvmetad cache would be left incorrect.
Now, disable lvmetad before the restore begins, and then
rescan to populate lvmetad from disk after restore has
written the new VG to disk.
This fixes a problem in commit ae0a8740c. The problem
in that commit was that all existing PVs are initially
dropped from lvmetad. This works if the VG is updated
at the end, which replaces the dropped PVs, but if the
rescan finds that the VG seqno is unchanged, it leaves
the cached VG in place. So, we should only drop the
existing PVs in lvmetad when the VG is going to be updated.
A number of places are working on a specific dev when they
call lvmcache_info_from_pvid() to look up an info struct
based on a pvid. In those cases, pass the dev being used
to lvmcache_info_from_pvid(). When a dev is specified,
lvmcache_info_from_pvid() will verify that the cached
info it's using matches the dev being processed before
returning the info. Calling code will not mistakenly
get info for the wrong dev when duplicate devs exist.
This confusion was happening when scanning labels when
duplicate devs existed. label_read for the first dev
would add an info struct to lvmcache for that dev/pvid.
label_read for the second dev would see the pvid in
lvmcache from first dev, and mistakenly conclude that
the label_read from the second dev can be skipped
because it's already been done. By verifying that the
dev for the cached pvid matches the dev being read,
this mismatch is avoided and the label is actually read
from the second duplicate.
If a command gets stuck during an lvmetad update, lvmetad
will cancel that update after the timeout. The next command
to check the lvmetad will see that lvmetad needs to be
populated because lvmetad will return token of "none" after
a timed out update (same as when lvmetad is not populated
at all after starting.)
If a command gets an error during an lvmetad update, it
will now just quit and leave its updating token in place.
That update will be cancelled after the timeout.
This refactors the code for autoactivation. Previously,
as each PV was found, it would be sent to lvmetad, and
the VG would be autoactivated using a non-standard VG
processing function (the "activation_handler") called via
a function pointer from within the lvmetad notification path.
Now, any scanning that the command needs to do (scanning
only the named device args, or scanning all devices when
there are no args), is done first, before any activation
is attempted. During the scans, the VG names are saved.
After scanning is complete, process_each_vg is used to do
autoactivation of the saved VG names. This makes pvscan
activation much more similar to activation done with
vgchange or lvchange.
The separate autoactivate phase also means that if lvmetad
is disabled (either before or during the scan), the command
can continue with the activation step by simply not using
lvmetad and reverting to disk scanning to do the
activation.
If a command begins repopulating the lvmetad cache,
and fails part way through, it should set the disabled
state in lvmetad so other commands don't use bad data.
If a subsequent scan succeeds, the disabled state is
cleared.
When command is not using lvmetad because
use_lvmetad=0 in the config, but the lvmetad
pidfile exists, print a warning (previously
this checked for the socket existing instead
of the pidfile existing.)
The lvmetad connection is created within the
init_connections() path during command startup,
rather than via the old lvmetad_active() check.
The old lvmetad_active() checks are replaced
with lvmetad_used() which is a simple check that
tests if the command is using/connected to lvmetad.
The old lvmetad_set_active(cmd, 0) calls, which
stopped the command from using lvmetad (to revert to
disk scanning), are replaced with lvmetad_make_unused(cmd).
After a device rescan that repopulates lvmetad,
if no reason for disabling lvmetad was seen
(lvm1 metadata or duplicate PVs), then clear
the disabled flag in lvmetad. This allows
commands to resume using the lvmetad cache
after the cause for disabling it has been removed.
Commands already check if the lvmetad token is valid,
and if not, they rescan devices to repopulate lvmetad
before running. Now, in addition to checking the
lvmetad token, they also check if the lvmetad disabled
flag is set. If so, they do not use the lvmetad cache
and revert to disk scanning.
A global flag in lvmetad indicates it has been disabled.
Other flags indicate the reason it was disabled.
These flags can be queried using get_global_info.
The lvmetactl debugging utility can set and clear the
disabled flag in lvmetad. Nothing else sets the
disabled flag yet.
Commands will check these flags after connecting to
lvmetad. If the disabled flag is set, the command
will not use the lvmetad cache, but revert to disk
scanning.
To test this feature:
$ lvmetactl get_global_info
response = "OK"
global_invalid = 0
global_disable = 0
disable_reason = "none"
token = "filter:3041577944"
$ vgs
(should report VGs from lvmetad)
$ lvmetactl set_global_disable 1
$ lvmetactl get_global_info
response = "OK"
global_invalid = 0
global_disable = 1
disable_reason = "DIRECT"
token = "filter:3041577944"
$ vgs
WARNING: Not using lvmetad because the disable flag was set directly.
(should report VGs without contacting lvmetad)
$ lvmetactl set_global_disable 0
$ vgs
(should report VGs from lvmetad)
Move checking the lvmetad state, and the possible rescan,
out of lvmetad_send() to the start of the command.
Previously, the token mismatch and rescan would occur
within lvmetad_send() for some other request. Now,
the token mismatch is detected earlier, so the
rescan can be done before the main command is in
progress. Rescanning deep within the processing of
another command will disturb the lvmcache state of
that other command.
A rescan already exists at the start of the command
for the case where foreign VGs are going to be read.
This same rescan is now also performed when there is
an lvmetad token mismatch (from a changed global_filter).
The commands pvscan/vgscan/lvscan/vgimport are excluded
from this preemptive checking/rescanning for lvmetad
because they want to do rescanning themselves explicitly.
If rescanning devices fails, then lvmetad has not been
correctly repopulated and should not be used, so make
the command revert to not using lvmetad.
Since we already check in few other places 'info' is not NULL,
do the same for others - however when info would be NULL
it more or less looks like internal error.
When not using lvmetad, this uses the system_id field in
the cached vginfo structs that are populated during a scan.
When using lvmetad, this requests the VG from lvmetad, and
checks the system_id field in the returned metadata.
When the command already knows both the vgid and vgname,
it should send both to lvmetad for a more exact request,
and it can save lvmetad the work of a name lookup.
Use 'mda' instead of NULL to quite Coverity warn.
However this code seems to be actually not even possible to hit.
With proper analysis it may possibly be dropped from code to
simplify logic.
When the command gets a list of alternate devices
from lvmetad, log each one directly. This is not
the same as the warnings when adding lvmcache,
which are related to which duplicate is preferred.
If lvmlockd is running, lvmetad is configured (use_lvmetad=1),
but lvmetad is not running, then commands will seg fault
when trying to send a message to lvmetad.
The difference is lvmetad being "active", not just "used".
