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Recognize DM_SUBSYSTEM_UDEV_FLAG0 which for LVM is the "LVM_NOSCAN"
flag that causes the scanning to be skipped (mainly blkid) and
also directs all the foreign rules to be skipped as well.
Important thing here is that the "watch" udev rules is still set
as well as the /dev/disk/by-id content created (which does not
require any scanning to be done). Also, the flag is dropped on
any subsequent event and scanning done...
This patch fixes the way the special devices are handled
(special in this context means that they're not usable
after the usual ADD event like other generic devices):
- DM and MD devices are pvscanned only when they are just set up.
This is the first CHANGE event that makes the device usable
(the DM_UDEV_PRIMARY_SOURCE_FLAG is set for DM and the
md/array_state sysfs attribute is present for MD).
Whether the device is activated is remembered via
DM_ACTIVATED (for DM) and LVM_MD_PV_ACTIVATED (for MD)
udev environment variable. This is then used to decide
whether we should fire the pvscan on ADD event to
support coldplugging. For any (artificial) ADD event
generated during coldplug, the device must be already
set up properly to fire the pvscan on it.
- Similar for loop devices. For loop devices, only CHANGE
events are relevant (so there's a CHANGE after the loop
device is set up as well as detached). Whether the loop
has just been activated is detected via loop/backing_file
sysfs attribute presence. The activation state is remembered
via LVM_LOOP_PV_ACTIVATED udev environment variable.
- Do not pvscan multipath device components (underlying paths).
- Do not pvscan RAID device components.
- Also, set LVM_SCANNED="1" udev environment variable for
debug purposes (it's visible in the lvmdump -u that takes
the current udev database). This variable is set once
the pvscan is triggered.
The table below summarises when the pvscan is triggered
(marked with X, X* means fire only if the special dev is properly set up):
| real ADD | real CHANGE | artificial ADD | artificial CHANGE | remove
=============================================================================
DM | | X | X* | | X
MD | | X | X* | |
loop | | X | X* | |
other | X | | X | | X
In stacked environment where we have a PV layered on top of a
snapshot LV and then removing the LV, lvmetad still keeps information
about the PV:
[0] raw/~ $ pvcreate /dev/sda
Physical volume "/dev/sda" successfully created
[0] raw/~ $ vgcreate vg /dev/sda
Volume group "vg" successfully created
[0] raw/~ $ lvcreate -L32m vg
Logical volume "lvol0" created
[0] raw/~ $ lvcreate -L32m -s vg/lvol0
Logical volume "lvol1" created
[0] raw/~ $ pvcreate /dev/vg/lvol1
Physical volume "/dev/vg/lvol1" successfully created
[0] raw/~ $ lvremove -ff vg/lvol1
Logical volume "lvol1" successfully removed
[0] raw/~ $ pvs
No device found for PV BdNlu2-7bHV-XcIp-mFFC-PPuR-ef6K-yffdzO.
PV VG Fmt Attr PSize PFree
/dev/sda vg lvm2 a-- 124.00m 92.00m
[0] raw/~ $ pvscan --cache --major 253 --minor 3
Device 253:3 not found. Cleared from lvmetad cache.
This is because of the reactivation that is done just before
snapshot removal as part of the process (vg/lvol1 from the example above).
This causes a CHANGE event to be generated, but any scan done
on the LV does not see the original data anymore (in this case
the stacked PV label on top) and consequently the ID_FS_TYPE="LVM2_member"
(provided by blkid scan) is not stored in udev db anymore for the LV.
Consequently, the pvscan --cache is not run anymore as the dev is not
identified as LVM PV by the "LVM2_member" id - lvmetad loses this info
and still keeps records about the PV.
We can run into a very similar problem with erasing the PV label directly:
[0] raw/~ $ lvcreate -L32m vg
Logical volume "lvol0" created
[0] raw/~ $ pvcreate /dev/vg/lvol0
Physical volume "/dev/vg/lvol0" successfully created
[0] raw/~ $ dd if=/dev/zero of=/dev/vg/lvol0 bs=1M
dd: error writing '/dev/vg/lvol0': No space left on device
33+0 records in
32+0 records out
33554432 bytes (34 MB) copied, 0.380921 s, 88.1 MB/s
[0] raw/~ $ pvs
PV VG Fmt Attr PSize PFree
/dev/sda vg lvm2 a-- 124.00m 92.00m
/dev/vg/lvol0 lvm2 a-- 32.00m 32.00m
[0] raw/~ $ pvscan --cache --major 253 --minor 2
No PV label found on /dev/vg/lvol0.
This patch adds detection of this change from ID_FS_LABEL="LVM2_member"
to ID_FS_LABEL="<whatever_else>" and hence informing the lvmetad
about PV being gone.
