[systemd-devel] prevent unmount of single partitions on shutdown

[Colin Guthrie]

'Twas brillig, and Zbigniew Jędrzejewski-Szmek at 21/08/13 14:17 did
gyre and gimble:
> On Wed, Aug 21, 2013 at 06:03:34PM +0800, Tom Gundersen wrote:
>> > On Wed, Aug 21, 2013 at 5:56 PM, Colin Guthrie <gmane at colin.guthr.ie> wrote:
>>> > > 'Twas brillig, and Zbigniew Jędrzejewski-Szmek at 21/08/13 04:38 did
>>> > > gyre and gimble:
>>>> > >> On Wed, Aug 21, 2013 at 05:21:59AM +0200, Stephan Raue wrote:
>>>>> > >>> Hi,
>>>>> > >>>
>>>>> > >>> i try to port systemd on a own embedded OS which is stored in a
>>>>> > >>> squashfs file. This file is on a fat partition (later mounted as
>>>>> > >>> /flash) on the drive.
>>>>> > >>>
>>>>> > >>> In our own initramfs (which dont uses systemd) /flash will be
>>>>> > >>> mounted and then the Squashfs file as /sysroot. later we do a
>>>>> > >>> switch_root and start systemd. On shutdown systemd trys now (5
>>>>> > >>> times) to unmount /flash and times out later with a error message.
>>>>> > >>> This delays the shutdown/reboot much. Systemd also trys to cleanup
>>>>> > >>> /dev/loop0. I need to prevent systemd to unmount /flash and clean
>>>>> > >>> /dev/loop0 (which is the / mount from the squashfs file).
>>>>> > >>>
>>>>> > >>> can i actually prevent this in some way and if nout could i request
>>>>> > >>> a feature to add a mount option which if avaible prevents systemd
>>>>> > >>> from unmounting single partitions and cleanup /dev/loopX if its
>>>>> > >>> still mounted as / ? I need this as mount option or a systemd unit
>>>>> > >>> file but for fstab based systems it would be usefull as a fstab
>>>>> > >>> option too (we dont use fstab)
>>>> > >> I don't think it's possible currently with fstab. But with
>>>> > >> a mount unit, I think
>>>> > >>   DefaultDependencies=no
>>>> > >>   RequiredBy=-.mount
>>>> > >> should work. Have you tried something like that?
>>> > >
>>> > > Hmm, I thought the umount logic was such that it just tries to unmount
>>> > > everything from/proc/mounts rather than looking at units etc.
>
> OTOH, if systemd manages to unmount something on top of which another 
> filesystem is mounted, is a kernel bug, no?

I would say so yes, but that's not what's happening here unless I
misunderstand something?

That said, I guess the umount loop itself shouldn't delay the reboot as
the commands there shouldn't take much time to fail (in theory at least)
so perhaps your sugguestion would indeed solve the delay problem.

Col


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Colin Guthrie
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