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Rewrite kdump's udev rules

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According to udev's man page, PROGRAM is either used to determine
device's name or whether the device matches the rule. So we should
use RUN insteand. Meanwhile, both RUN / PROGRAM only accepts very
short-running foreground tasks, but kdump restart may take a long
time if there are any device changes that will lead to image rebuild,
which may lead to buggy behavior.

On the other hand, memory / CPU hot plug should never trigger a
initramfs rebuild.

To solve this problem, we will use new introduced "kdumpctl reload"
instead, and use systemd-run to create a transient service unit for
the reload and run it in no-block mode, so udev won't be blocked by
anything.

We need to make systemd-run execute in non-blocking mode, and do not
synchronously wait for the operation to finish, because udev expect
the command line in RUN to be finished immediately, however, kdumpctl
reload may take 0.5-1s for an ordinary reload, or even slower on some
machines. So we give systemd-run an explicit --no-block option to run
in non-blocking mode. Without --no-blocking, systemd-run will verify,
enqueue and wait for the operation to finish. By using the --no-block
option, systemd-run will only verify and enqueue the unit then
return. In this way, we make sure the command is executed
asynchronously, and the status will be monitored and logged by
systemd, which is reliable and non-blocking.

Another thing to mention is that --no-block is only needed after
systemd-v220, before v220 systemd-run uses non-blocking mode by
default and --no-block option is not available on earlier systemd
versions.

Also reformat the udev rules to a more maintanceable format.

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>
This commit is contained in:
Kairui Song 2018-10-24 16:58:51 +08:00
parent b34ce3a7b4
commit 227c18506c
1 changed files with 12 additions and 4 deletions
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16
98-kexec.rules
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@ -1,4 +1,12 @@
SUBSYSTEM=="cpu", ACTION=="add", PROGRAM="/bin/systemctl try-restart kdump.service"
SUBSYSTEM=="cpu", ACTION=="remove", PROGRAM="/bin/systemctl try-restart kdump.service"
SUBSYSTEM=="memory", ACTION=="online", PROGRAM="/bin/systemctl try-restart kdump.service"
SUBSYSTEM=="memory", ACTION=="offline", PROGRAM="/bin/systemctl try-restart kdump.service"
SUBSYSTEM=="cpu", ACTION=="add", GOTO="kdump_reload"
SUBSYSTEM=="cpu", ACTION=="remove", GOTO="kdump_reload"
SUBSYSTEM=="memory", ACTION=="online", GOTO="kdump_reload"
SUBSYSTEM=="memory", ACTION=="offline", GOTO="kdump_reload"
GOTO="kdump_reload_end"
LABEL="kdump_reload"
RUN+="/usr/bin/systemd-run --no-block /usr/bin/kdumpctl reload"
LABEL="kdump_reload_end"