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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.
The new lvm2-pvscan@.service is responsible for on-demand execution
of "pvscan --cache --activate ay" which causes lvmetad to be
updated and LVM activation done if the VG is complete.
Also, use udev-systemd mechanism to instantiate the job as the
lvm2-pvscan@$devnode.service on each newly appeared PV in the system.
This prevents the background job to be killed (that would happen
if it was directly forked from udev rule - this behaviour is seen
in recent versions of udev with the help of systemd that can track
detached processes - the detached process would still be in the same
cgroup).
To enable this official udev-systemd protocol for instantiating
background jobs, use new --enable-udev-systemd-background-jobs
configure switch (it's disabled by default). This option is highly
recommended wherever systemd is used!
Remove executable path detection in udev rules and use sbindir that
is configured, but still provide the original functionality by means
of 'configure --enable-udev-rule-exec-detection'.
Normally, the exec path for the tools called in udev rules should
not differ from the sbindir used, however, there are cases this is
necessary. For example different environments could be assembled
in a way that these path differ for some reason (distribution installer,
initrd ...).
This functionality is kept for compatibility only. Any environment
moving the binaries around and using different paths should be fixed
eventually!
Why using the order 69:
- Storage processing in general happens in 60-persistent-storage.rules,
including the blkid call that adds some usable information we can use
for filtering and speedup (these rules are part of upstream udev and
the order is preserved on most distros)
- There's still some other storage-related processing done after
60-persistent-storage.rules in general. These might add some detailed
storage-related information we might use to filter devices effectively
(e.g. MD udev rules, ...).
- We need lvmetad rules to be processed before any consumers can use the
output - so the metadata cache is ready soon enough (e.g. udisks rules).
- There's no official (upstream udev) document about assigning the order,
so this number is chosen in best belief it will suit all scenarios.
Fix unwanted modification of $(top_builddir)/make.tmpl.
Using dependency rules to install rules for udev.
There is minor problem, with concurent usage of builddir
and srcdir could lead to missuse of 10-dm.rules which
could be found in VPATH from different builddir.
However current solution uses intermediate target so
the generated 10-dm.rules exists only for short period of time
during make install execution.
Usage of VPATH makes troubles when used within $(builddir).
Not only source files are being found through VPATH,
but targets as well. (make --debug=v)
Thus if user builds the code in $(srcdir) and also in some $(builddir)
he gets mangled results as some generated files (i.e. .export.sym)
are 'reused' from $(srcdir) instead of $(builddir).
This patch switches to use vpath were we could explicitly name
suffixes that should be looked via vpath - we must take care,
we do not generate files with these suffixes:
.c, .in, .po, .exported_symbols
- we have these levels when the udev rules are processed:
10-dm.rules --> [11-dm-<subsystem>.rules] --> [12-dm-permissions.rules] -->
13-dm-disk.rules --> [...all the other foreign rules...] --> 95-dm-notify.rules
- each level can be disabled now by
DM_UDEV_DISABLE_{DM, SUBSYSTEM, DISK, OTHER}_RULES_FLAG
- add DM_UDEV_DISABLE_DM_RULES_FLAG to disable 10-dm.rules
- add DM_UDEV_DISABLE_OTHER_RULES_FLAG to disable all the other (non-dm) rules.
We cutoff these rules by using the 'last_rule', so this one should really be
used with great care and in well-founded situations. We use this for lvm's
hidden and layer devices now.
- add a parameter for add_dev_node, rm_dev_node and rename_dev_node so it's
possible to switch on/off udev checks
- use DM_UDEV_DISABLE_DM_RULES_FLAG and DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG
if there's no cookie set and we have resume, remove and rename ioctl.
This could happen when someone uses the libdevmapper that is compiled with
udev_sync but the software does not make use of it. This way we can switch
off the rules and fallback to libdevmapper node creation so there's no
udev/libdevmapper race.
