RE: [Xen-devel] [PATCH v2 2/4] xenbus: limit when state is forced to closed

Durrant, Paul
2019-12-11T13:29:29Z

> -----Original Message-----
> From: Jürgen Groß <jgross@suse.com>
> Sent: 11 December 2019 10:21
> To: Durrant, Paul <pdurrant@amazon.com>; Roger Pau Monné
> <roger.pau@citrix.com>
> Cc: xen-devel@lists.xenproject.org; linux-kernel@vger.kernel.org; Stefano
> Stabellini <sstabellini@kernel.org>; Boris Ostrovsky
> <boris.ostrovsky@oracle.com>
> Subject: Re: [Xen-devel] [PATCH v2 2/4] xenbus: limit when state is forced
> to closed
>
> On 11.12.19 11:14, Durrant, Paul wrote:
> >> -----Original Message-----
> >> From: Roger Pau Monné <roger.pau@citrix.com>
> >> Sent: 11 December 2019 10:06
> >> To: Durrant, Paul <pdurrant@amazon.com>
> >> Cc: xen-devel@lists.xenproject.org; linux-kernel@vger.kernel.org;
> Juergen
> >> Gross <jgross@suse.com>; Stefano Stabellini <sstabellini@kernel.org>;
> >> Boris Ostrovsky <boris.ostrovsky@oracle.com>
> >> Subject: Re: [Xen-devel] [PATCH v2 2/4] xenbus: limit when state is
> forced
> >> to closed
> >>
> >> On Tue, Dec 10, 2019 at 11:33:45AM +0000, Paul Durrant wrote:
> >>> If a driver probe() fails then leave the xenstore state alone. There
> is
> >> no
> >>> reason to modify it as the failure may be due to transient resource
> >>> allocation issues and hence a subsequent probe() may succeed.
> >>>
> >>> If the driver supports re-binding then only force state to closed
> during
> >>> remove() only in the case when the toolstack may need to clean up.
> This
> >> can
> >>> be detected by checking whether the state in xenstore has been set to
> >>> closing prior to device removal.
> >>>
> >>> NOTE: Re-bind support is indicated by new boolean in struct
> >> xenbus_driver,
> >>> which defaults to false. Subsequent patches will add support to
> >>> some backend drivers.
> >>
> >> My intention was to specify whether you want to close the
> >> backends on unbind in sysfs, so that an user can decide at runtime,
> >> rather than having a hardcoded value in the driver.
> >>
> >> Anyway, I'm less sure whether such runtime tunable is useful at all,
> >> so let's leave it out and can always be added afterwards. At the end
> >> of day a user wrongly doing a rmmod blkback can always recover
> >> gracefully by loading blkback again with your proposed approach to
> >> leave connections open on module removal.
> >>
> >> Sorry for the extra work.
> >>
> >
> > Does this mean you don't think the extra driver flag is necessary any
> more? NB: now that xenbus actually takes module references you can't
> accidentally rmmod any more :-)
>
> I'd like it to be kept, please.
>

Ok. I'll leave this patch alone then.

Paul

> Juergen