On Monday 25 August 2014 at 19:42:21, Lennart Poettering wrote: > On Mon, 25.08.14 02:16, Ivan Shapovalov ([email protected]) wrote: > > > This patchset allows systemd to parse resume= kernel command line parameter > > and initiate resume from the specified device. > > > > It adds: > > - a 'systemd-resume' tool which takes path to a device node and > > writes its major:minor to /sys/power/state; > > - a corresponding '[email protected]' templated unit; > > - a 'systemd-resume-generator' generator which parses the kernel command > > line > > and instantiates the unit as necessary. > > > > This functionality already exists in-kernel, but only for "/dev/sdXY"-style > > pathes. Implementing it in userspace allows to use arbitrary udev-created > > symlinks, e. g. persistent block device pathes ("/dev/disk/by-foo/bar"). > > > > Userspace parsing of resume= kernel command line parameter has been > > traditionally done in initramfs via shell scripts (for Arch Linux, this is > > "resume" mkinitcpio hook), so I feel that this feature has its place within > > systemd. > > > > Due to the nature of hibernation, the resume unit must be activated before > > any modifications to filesystems take place. This can happen only in > > initramfs > > before mounting anything. > > > > So, first patch orders all non-root fsck after local-fs-pre.target, which in > > turn allows to order the resume unit before those fsck instances. > > > > Second and third patches add the tool, the unit and the generator. > > > > There are some issues with this implementation. > > > > - legacy usr.mount is not automatically ordered after local-fs-pre.target, > > so [email protected] has to be manually ordered before it; > > Not following here. We do not really support /usr split out unless it is > already mounted in the initrd. But in the initrd its called > "sysroot-usr.mount"... To me this doesn't look like something to do here?
Theoretically it is possible to have initramfs's /usr split out.
I know that it sounds crazy, but if someone will do this, they will lose their
data if usr.mount not properly handled.
>
> > - systemd-udevd.service, which is needed for creating persistent block
> > device
> > symlinks, is transitively ordered after systemd-remount-fs.service via at
> > least systemd-udev-hwdb-update.service and systemd-sysusers.service.
> > Hence, if these units are present, an ordering cycle happens and resume is
> > impossible.
>
> Hmm? What's the cycle precisely? Not following?
systemd-remount.fs.service -> systemd-udev-hwdb-update.service ->
systemd-udevd.service
systemd-sysusers.service
Here, the arrow represents an "After=" dependency.
If either "systemd-udev-hwdb-update.service" or "systemd-sysusers.service"
becomes part of the transaction (== becomes included in the initramfs),
it becomes impossible for "[email protected]" to start after
"systemd-udevd.service". The outcome can vary:
- a 90 second wait for dev-disk-by\x2dfoo-bar.device and dependency failure
(if "After=systemd-udevd.service" has not been specified);
- an ordering cycle and removal of "[email protected]" from transaction
(if "After=systemd-udevd.service" has been specified, just as it is now).
Both situations are very unlikely (who would add usr.mount to initramfs? who
would add systemd-sysusers.service to initramfs?), but nevertheless possible.
--
Ivan Shapovalov / intelfx /
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