Re: [Xen-devel] [PATCH v1] tools/hotplug: convert proc-xen.mount to proc-xen.service

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Oct 26, 2017 at 05:25:36PM +0200, Olaf Hering wrote:
> An upcoming change in systemd will mount xenfs right away, along with
> all other system mounts. This improves the detection of the
> virtualization environment, which is currently racy. Some parts of
> systemd rely on the presence of /proc/xen/capabilities, which will only
> exist if xenfs is mounted. Since xenfs is mounted by the proc-xen.mount
> unit, it will be processed very late. Other units may be processed
> earlier, and if they make use of ConditionVirtualization*= failures may
> occour.
> 
> Unfortunately mounting xenfs by systemd as an API filesystem will lead
> to errors when proc-xen.mount is processed. Since that mount point
> already exists the unit is considered as failed, and other units that
> depend on proc-xen.mount will not start. To avoid this the existing
> proc-xen.mount will be converted into proc-xen.service, which just
> mounts xenfs manually. All dependencies are updated by this change.
> 
> The existing conditionals in proc-xen.mount will prevent failures with
> existing systemd based installations:
> ConditionPathExists=!/proc/xen/capabilities will prevent execution with
> a new systemd that mounts xenfs. And this conditional, in combination
> with ConditionPathExists=/proc/xen, will trigger execution with an old
> systemd.
> 
> An absolute path to the mount binary has to be used. /bin/mount is
> expected to be universally available, nowaways it is a symlink to
> /usr/bin/mount.
> 
> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>

The code itself looks OK at a glance.

What is unsaid is that we need to backport this to older Xen releases so
that old Xen can work with new systemd.

Ian and Jan?

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