[systemd-devel] Implementing resume from hibernation as a systemd unit file

[Ivan Shapovalov]

On Thursday 21 August 2014 at 01:03:20, Lennart Poettering wrote:	
> [...]
> > > 
> > > ...missing sysroot's fsck, as well as any other x-initrd mounts and their fsck instances.
> > > 
> > > Seems that sysroot.mount alone isn't sufficient.
> > 
> > ...Anything on this?
> > 
> > Should we add yet another passive target(s), something like fsck-pre? I don't
> > actually know what is the best way to tackle this. The resume unit shall be
> > activated before any writes to any block devices, including fsck, cryptsetup
> > and whatever else.
> 
> Hmm, so I though a bit about this, and I think we should make the
> following changes to systemd:
> 
> a) move local-fs-pre.target before all the fsck. This way we can make
>    use of it as a barrier against modifications of any fs.

...all fsck except the systemd-fsck-root.service, right? It's already ordered
before local-fs-pre.target.

Makes sense; then the resume unit will be

    Wants=local-fs-pre.target
    Before=local-fs-pre.target systemd-fsck-root.service systemd-remount-fs.service shutdown.target
    ConditionPathIsReadWrite=!/

However, this breaks when there is a legacy /usr mount without fsck...
src/core/mount.c:mount_add_default_dependencies() does not add
After=local-fs-pre.target if the mount in question is / or /usr.

Hence, the legacy /usr mount is missed by this scheme.

> 
> 
> b) introduce initrd-fs-pre.target that then plays a similar role, but in
>    the initrd.

Is it neeeded? IIUC, local-fs-pre.target can be used in initramfs as well,
the default dependency on this target is still generated on all mounts.
(except in-initramfs /usr, see the above problem)

> 
> A service that wants to run before any fs is touched should then order
> itself before both and everything should be good.
> 
> If this makes sense, I would be happy to take a patch.
> 
> I'd be willing to merge a good patch for a generator + mini-tool that
> parse the resume= option into systemd as well, btw.

I've already implemented the generator and resume tool prototype. Sure, when we
solve the dependencies problem, I'll submit this for inclusion.

-- 
Ivan Shapovalov / intelfx /
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