Re: [RFC] kernel: xenfs parameter to hide deprecated files

[Juergen Gross <jgross@xxxxxxxx>]

On 23.02.22 19:08, James Dingwall wrote:
> Hi,
>
> I have been investigating a very intermittent issue we have with xenstore
> access hanging.  Typically it seems to happen when all domains are stopped
> prior to a system reboot.  xenstore is running in a stubdom and using the
> hypervisor debug keys indicates the domain is still there.
Could it be dom0 shutdown handling is unloading some modules which are
needed for Xenstore communication? E.g. xen-evtchn?

> I have come across some old list threads which suggested access via
> /proc/xen/xenbus could cause problems but it seems patches went in to the
> kernel for 4.10.  However to eliminate this entirely as a possibility
> I came up with this kernel patch to hide deprecated entries in xenfs.
I don't see how this patch could help.

libxenstore is using /dev/xen/xenbus if it is available. So the only
case where your patch would avoid accessing /proc/xen/xenbus would be
if /dev/xen/xenbus isn't there. But this wouldn't make Xenstore more
reactive, I guess. ;-)

> I found this old thread for a similar change where the entries were made
> conditional on kernel config options instead of a module parameter but
> this was never merged.
>
> https://lkml.org/lkml/2015/11/30/761
>
> If this would be a useful feature I would welcome feedback.
I'm not sure how helpful it is to let the user specify a boot parameter
for hiding the files. It will probably not get used a lot.


Juergen

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