On 04/08/14 at 06:02pm, Vivek Goyal wrote: > On Tue, Apr 08, 2014 at 02:14:33AM +0200, Zbigniew Jędrzejewski-Szmek wrote: > > [..] > > > > > Defining a new target which by default waits for all the local fs > > > > > target > > > > > sounds interesting. Again, I have the question, what will happen to > > > > > local-fs-all.target if some device does not show up and say one of the > > > > > mounts specified in /etc/fstab fails. > > It result is different for Requires= and for Wants=. Iff there's a chain > > of Requires= from the failing unit (.device in this case) to the target unit > > it will fail. Otherwise, it'll just be delayed. If, as I suggested above > > local-fs-all.target > > would have Requires= on the .mount units, then your unit could still have > > Wants=/After=local-fs-all.target, and it'll be started even if some mounts > > fail. > > Thanks now I understand the difference between Requires= and Wants= > better. > > > > > > > > What we want is. > > > > > > > > > > - Wait for all devices to show up as specified in /etc/fstab. Run fsck > > > > > on devices. Mount devices to mount points specified. > > > > > > > > > > - If everything is successful, things are fine and local-fs-all.target > > > > > will be reached. > > > > > > > > > > - If some device does not show up, or if fsck fails or mount fails, > > > > > still > > > > > local-fs-all.target should reach so that kdump module can detect > > > > > that > > > > > failure happened and can take alternative action. > > Alternatively, you can specify a soft depenendency on local-fs-all.target by > > using Wants=local-fs-all.target. I think this is preferable, because we want > > local-fs-all.target to be as similar as possible to local-fs.target, which > > has Requires= on the mount points. > > > > With this caveat, this should all be satisfied with my proposal. > > Agreed. We could define Wants=local-fs-all.target and that would make > sure that our unit will be started even if local-fs-all.target fails. > > > > > > > You can use OnFailure= to define unit(s) started when > > > > local-fs-all.target fails. But it sounds like you are not really > > > > interested in *all* filesystems, but in specific fileststems defined in > > > > kdump configuration. > > > > > > Kdump scripts registers with dracut as pre-pivot hook. And I believe > > > that in initramfs environments /etc/fstab does not contain all > > > filesystems. It prmarily contains root and any file system specified > > > on dracut command line using --mount option during initramfs generation. > > > > > > So my understanding that given the fact that /etc/fstab is minimal in > > > initramfs, we should be fine waiting for all the fs specified. > > > > > > Given the fact that we run under dracut pre-pivot hook callback, I think > > > dracut-pre-pivot.service wil have to create a dependency to run after > > > local-fs-all.target is reached. > > Hm, maybe. It would be good to get some input from Harald here. > > This is pretty specialized, so maybe it'd be better to have a separate unit > > positioned before or after or parallel to dracut-pre-pivot.service. > > I am just thinking loud now. Taking a step back and going back to > figure out why did we introduce "nofail" to begin with. > > If I go through kexec-tools logs, it says "nofail" was introduced > otherwise we never reach initrd.target. I am wondering why that's the > case. Current initrd.target seems to have following. > > [Unit] > Description=Initrd Target > Requires=basic.target > Conflicts=rescue.service rescue.target > After=basic.target rescue.service rescue.target > AllowIsolate=yes > OnFailure=emergency.target > OnFailureIsolate=yes > ConditionPathExists=/etc/initrd-release
dracut doesn't use this initrd.target. It uses the stock one from systemd: [Unit] Description=Initrd Default Target Documentation=man:systemd.special(7) OnFailure=emergency.target OnFailureIsolate=yes ConditionPathExists=/etc/initrd-release Requires=basic.target Wants=initrd-root-fs.target initrd-fs.target initrd-parse-etc.service After=initrd-root-fs.target initrd-fs.target basic.target rescue.service rescue.target AllowIsolate=yes In sysroot.mount context, if we don't use "nofail" in case of root disk failure, we will never reach initrd-root-fs.target and hence we never reach initrd.target and dracut-pre-povit.service never get a chance to start. > > So it Requires=basic.target. Now let us say basic.target fails, then > I am assuming emergency.target will be activated. And if we hook into > emergency-shell binary and make it run a registered error handler if > it is available, then kdump can drop its handler and take action on > failure. > > IOW, what if we stop passing "nofail". Then local-fs.target practically > becomes local-fs-all.target. Either services will start just fine (after > a wait for deivces to show up). Or units will start failing and if boot > can't cointinue then somewhere we will fall into emergency shell and > then emergency shell will call into kdump handler. > > This is assuming that we have designed boot path in such a way that > most of the time we will not do infinite wait (until and unless user > asked us to do to. (x-systemd.device-timeout=0). So either we will wait > for finite amount of time and then fail some services but continue to > boot. And along the path if we can't make progress then we will drop into > emergency shell. > > If above assumption is right, then hooking into emergency shell logic > in initramfs should provide what I am looking for. I think that's right. Stop passing "nofail" and install own error handler should be the right thing to do. Thanks WANG Chao _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
