udev+systemd: refine lvm2-pvscan@.service to better track device existence

When using ENV{SYSTEMD_WANTS}=lvm2-pvscan@... to instantiate a service
for lvmetad scan when the new PV appears in the system, the service
is started and executed. However, to track device removal, we need
to bind it (the "BindsTo" systemd directive) to a certain .device
systemd unit.

In default systemd setup, the device is tracked by it's name and
sysfs path (there's normally a sysfs path .device systemd unit for
a device and then the device name .device unit as an alias for it).
Neither of these two is useful for lvmetad update as we need to bind
it to device's <major>:<minor> pair.

The /dev/block/<major>:<minor> is the essential symlink under /dev
that exists for each block device (created by default udev rules
provided by udev directly). So let's use this as an alias for
the device's .device unit as well by means of "ENV{SYSTEMD_ALIAS}"
declaration within udev rules which systemd understands (this will
create a new alias "dev-block-<major>:<minor>.device".

Then we can easily bind the "dev-block-<major>:<minor>" device
systemd unit with instantiated lvm2-pvscan@<major>:<minor>.service.
So once the device is removed from the systemd, the
lvm-pvscan@<major>:<minor>.service executes it's ExecStop action
(which in turn notifies lvmetad about the device being gone).

This completes the udev-systemd-lvmetad interaction then.

diff --git a/WHATS_NEW b/WHATS_NEW
index df81923ffd8eb733aa16082e9892873ae603c7f0..2d7792b92ee8bd3b4e6dfb3adc5f1d89954cff2c 100644 (file)
--- a/WHATS_NEW
+++ b/WHATS_NEW
@@ -1,5 +1,6 @@
 Version 2.02.104
 ===================================
+  Add dev-block-<major>:<minor>.device systemd alias for complete PV tracking.
   Use major:minor as short form of --major and --minor arg for pvscan --cache.
   Remove 2>/dev/null from three lvm commands executed by vgimportclone.
   Add configure --enable-udev-systemd-background-jobs.

diff --git a/scripts/lvm2_pvscan_systemd_red_hat@.service.in b/scripts/lvm2_pvscan_systemd_red_hat@.service.in
index 9d91b5ecb99f399f698858d68a07e06a87e4e36f..07ea5caca6aa7e0dac756f0a37bcf4f0639a053b 100644 (file)
--- a/scripts/lvm2_pvscan_systemd_red_hat@.service.in
+++ b/scripts/lvm2_pvscan_systemd_red_hat@.service.in
@@ -1,11 +1,14 @@
 [Unit]
-Description=LVM2 PV scan on %I
+Description=LVM2 PV scan on device %i
 Documentation=man:pvscan(8)
 DefaultDependencies=no
-After=lvm2-lvmetad.socket %i.device
+BindsTo=dev-block-%i.device
+After=lvm2-lvmetad.socket
 Before=shutdown.target
 Conflicts=shutdown.target
 
 [Service]
-Type=simple
-ExecStart=@sbindir@/pvscan --cache --activate ay %I
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=@sbindir@/pvscan --cache --activate ay /dev/block/%i
+ExecStop=/usr/sbin/pvscan --cache %i

diff --git a/udev/Makefile.in b/udev/Makefile.in
index fdf43df5edcb1d4bd0e8f286e25736449c386744..8f0dc8a7823219468643cbc850d6bbaf274551c6 100644 (file)
--- a/udev/Makefile.in
+++ b/udev/Makefile.in
@@ -47,7 +47,9 @@ BLKID_RULE=IMPORT{program}=\"${SBIN}\/blkid -o udev -p \$$tempnode\"
 endif
 
 ifeq ("@UDEV_SYSTEMD_BACKGROUND_JOBS@", "yes")
-PVSCAN_RULE=ENV{SYSTEMD_WANTS}=\"lvm2-pvscan@\$$devnode.service\"
+PVSCAN_RULE="ENV{SYSTEMD_ALIAS}=\"/dev/block/$$major:$$minor\" \
+            ENV{ID_MODEL}=\"LVM PV $$env{ID_FS_UUID_ENC} on /dev/$$name\" \
+            ENV{SYSTEMD_WANTS}=\"lvm2-pvscan@\$$devnode.service\""
 else
 PVSCAN_RULE=RUN\+\=\"$(LVM_EXEC)/lvm pvscan --background --cache --activate ay --major \$$major --minor \$$minor\", ENV{LVM_SCANNED}=\"1\"
 endif