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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.
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.
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 duplicate PVs are detected, set the disabled
flag so that commands will disable use of lvmetad.
This duplicate detection is done by lvmetad itself
when it's told about a single new PV with a PVID
that matches an existing PV on another device.
(This is different from the case where the command
is scanning all devices and detects the duplicate.)
Remove the "altdev" logic that attempted to keep
track of multiple devices for a single PV. It
is no longer used since lvmetad is disabled in
this case.
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.
In lookup, return a count of entries with the
same key rather than the value from a second
entry with the same key.
Using some slightly different names.
Simply use lookup_withval right away rather than doing a
standard lookup, checking for the wrong mapping, then
repeating with lookup_withval to get the right mapping.
If the data len is passed into the hash table
and saved there, then the hash table internals
do not need to assume that the data value is
a string at any point.
New hash table functions are added that allow for
multiple entries with the same key. Use of the
vgname_to_vgid hash table is converted to these
new functions since there are multiple entries
in vgname_to_vgid that have the same key (vgname).
When multiple VGs with the same name exist, commands
that reference only a VG name will fail saying the
VG could not be found (that error message could be
improved.) Any command that works with the select
option can access one of the VGs with -S vg_uuid=X.
vgrename is a special case that allows the first VG
name arg to be replaced by a uuid, which also works.
(The existing hash table implementation is not well
suited for handling this case, but it works ok with
the new extensions. Changing lvmetad to use its own
custom hash tables may be preferable at some point.)
Check for arg_vgid_lookup and arg_name_lookup not being NULL.
Drop checking arg_vgid and arg_name for NULL since they
are already dereference earlier - thus mostly must be NOT NULL.
(If that would be possible larger rework of this function would be
required).
update_metadata and pv_found update the cached metadata;
these are both reworked to improve the code, organize it
by each possible state and transition, make it much more
clear what's changing, add more error checking and
handling, and add comments.
The state and content of the cache (hash tables) does not
change (apart from some things that didn't work before),
and the communication to/from commands does not change.
The implementation and organization of the code making
the state changes does change significantly.
One detail related to the content of the cache does change:
different hash tables do not reference the same memory any more;
the target values in each hash table are allocated and freed
individually.
set_vg_info previously accepted only vg uuid,
now accept both vg uuid and vg name. If the
uuid is provided, it's used just as before,
but if the uuid is not provided, or if it's
not found, then fall back to using the vg
name if that is provided.
lib/format1/import-export.c:167: var_deref_op: Dereferencing null pointer "vg->lvm1_system_id"
lib/cache/lvmetad.c:1023: var_deref_op: Dereferencing null pointer "this"
daemons/lvmlockd/lvmlockd-core.c:2659: check_after_deref: Null-checking "act" suggests that it may be null, but it has already been dereferenced on all paths leading to the check
/daemons/lvmetad/lvmetad-core.c:1024: check_after_deref: Null-checking "pvmeta" suggests that it may be null, but it has already been dereferenced on all paths leading to the check
Add the ability to invalidate global or individual VG metadata.
The invalid state is returned to lvm commands along with the metadata.
This allows lvm commands to detect stale metadata from the cache and
reread the latest metadata from disk (in a subsequent patch.)
These changes do not change the protocol or compatibility between
lvm commands and lvmetad.
Global information
------------------
Global information refers to metadata that is not isolated
to a single VG , e.g. the list of vg names, or the list of pvs.
When an external system, e.g. a locking system, detects that global
information has been changed from another host (e.g. a new vg has been
created) it sends lvmetad the message: set_global_info: global_invalid=1.
lvmetad sets the global invalid flag to indicate that its cached data is
stale.
When lvm commands request information from lvmetad, lvmetad returns the
cached information, along with an additional top-level config node called
"global_invalid". This new info tells the lvm command that the cached
information is stale.
When an lvm command sees global_invalid from lvmated, it knows it should
rescan devices and update lvmetad with the latest information. When this
is complete, it sends lvmetad the message: set_global_info:
global_invalid=0, and lvmetad clears the global invalid flag. Further lvm
commands will use the lvmetad cache until it is invalidated again.
The most common commands that cause global invalidation are vgcreate and
vgextend. These are uncommon compared to commands that report global
information, e.g. vgs. So, the percentage of lvmetad replies containing
global_invalid should be very small.
VG information
--------------
VG information refers to metadata that is isolated to a single VG,
e.g. an LV or the size of an LV.
When an external system determines that VG information has been changed
from another host (e.g. an lvcreate or lvresize), it sends lvmetad the
message: set_vg_info: uuid=X version=N. X is the VG uuid, and N is the
latest VG seqno that was written. lvmetad checks the seqno of its cached
VG, and if the version from the message is newer, it sets an invalid flag
for the cached VG. The invalid flag, along with the newer seqno are saved
in a new vg_info struct.
When lvm commands request VG metadata from lvmetad, lvmetad includes the
invalid flag along with the VG metadata. The lvm command checks for this
flag, and rereads the VG from disk if set. The VG read from disk is sent
to lvmetad. lvmetad sees that the seqno in the new version matches the
seqno from the last set_vg_info message, and clears the vg invalid flag.
Further lvm commands will use the VG metadata from lvmetad until it is
next invalidated.
There are two reasons for this: first, this allows the client side to notice
that some PV has multiple devices associated with it and print appropriate
warnings. Second, if a duplicate device pops up and disappears, after this
change the original connection between the PV and device is not lost.
