[RFC] removing proc-xen.mount due to systemd change

[RFC] removing proc-xen.mount due to systemd change

[Vasilis Liaskovitis]

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Hello,


It is possible for systemd services to check for dom0 detection before xenfs gets mounted by proc-xen.mount. See this systemd bug report for an example:
https://github.com/systemd/systemd/issues/6442


Upstream systemd has accepted the patch for this: https://github.com/systemd/systemd/pull/6662,
which mounts xenfs at systemd init time i.e. making /proc/xen an API file.


However the issue now is that proc-xen.mount will refuse to mount /proc/xen as it an API file system, and the service will fail. This breaks xen, as other services depending on proc-xen.mount also fail.


What is the preferred way to deal with this in upstream xen?


- We can remove proc-xen.mount completely, for systems using systemd.


- any other options?


thank you,


- Vasilis



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Re: [RFC] removing proc-xen.mount due to systemd change

[Vasilis Liaskovitis]

Apologies for formatting. Here is my question in plain text:

There are systemd services that check for dom0 detection before xenfs
gets mounted by proc-xen.mount. See this systemd bug report for an
example:
https://github.com/systemd/systemd/issues/6442

Upstream systemd has accepted the patch for this: https://github.com/sy
stemd/systemd/pull/6662,
which mounts xenfs at systemd init time i.e. making /proc/xen an API
file.

However the issue now is that proc-xen.mount will refuse to mount
/proc/xen as it an API file system, and the service will fail. This
breaks xen, as other services depending on proc-xen.mount also
fail.

What is the preferred way to deal with this in xen?

- We can remove proc-xen.mount completely, for systems using systemd.

- any other options?

thank you,

- Vasilis


On Mon, 2017-10-02 at 11:21 +0200, Vasilis Liaskovitis wrote:
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> https://lists.xen.org/xen-devel

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Re: [RFC] removing proc-xen.mount due to systemd change

[Wei Liu]

On Mon, Oct 02, 2017 at 12:26:24PM +0200, Vasilis Liaskovitis wrote:
> Apologies for formatting. Here is my question in plain text:
> 
> There are systemd services that check for dom0 detection before xenfs
> gets mounted by proc-xen.mount. See this systemd bug report for an
> example:
> https://github.com/systemd/systemd/issues/6442
> 
> Upstream systemd has accepted the patch for this: https://github.com/sy
> stemd/systemd/pull/6662,
> which mounts xenfs at systemd init time i.e. making /proc/xen an API
> file.
> 
> However the issue now is that proc-xen.mount will refuse to mount
> /proc/xen as it an API file system, and the service will fail. This
> breaks xen, as other services depending on proc-xen.mount also
> fail.
> 
> What is the preferred way to deal with this in xen?
> 
> - We can remove proc-xen.mount completely, for systems using systemd.
> 

That would break Xen system using an older version of systemd, right?
I'm against such action.

> - any other options?

Can we just make the unit not fail? I.e. when it detects xenfs is
already mounted, it does nothing but reports success.

> 
> thank you,
> 
> - Vasilis
> 
> 
> On Mon, 2017-10-02 at 11:21 +0200, Vasilis Liaskovitis wrote:
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xen.org
> > https://lists.xen.org/xen-devel
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> https://lists.xen.org/xen-devel

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Re: [RFC] removing proc-xen.mount due to systemd change

[Franck Bui]

On 10/02/2017 12:35 PM, Wei Liu wrote:
> On Mon, Oct 02, 2017 at 12:26:24PM +0200, Vasilis Liaskovitis wrote:
>> - any other options?
> 
> Can we just make the unit not fail? I.e. when it detects xenfs is
> already mounted, it does nothing but reports success.
> 

Unfortunately that's currently not possible as systemd fails when
*loading* the mount unit.

Therefore whatever the conditions you put in the mount unit (to avoid
systemd starting it) won't be considered at all as systemd will refuse
to load a mount unit whose target path is part of the API file systems.

An indirection could be added, that is adding a simple service that
would require the mount unit and contains the conditions that would
prevent its starting if /proc/xen is already mounted but that doesn't
look pretty...

I think it would be better to continue the discussion here [1], as a
solution might require some changes on systemd side.

Thanks.


[1] https://github.com/systemd/systemd/issues/6442

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Re: [RFC] removing proc-xen.mount due to systemd change

[Franck Bui]

On 10/02/2017 03:55 PM, Franck Bui wrote:
> 
> I think it would be better to continue the discussion here [1], as a
> solution might require some changes on systemd side.
> 

Actually I continued the discussion here:
https://github.com/systemd/systemd/pull/6662

Feel free to join !

Thanks.

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