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

[Jürgen Groß <jgross@xxxxxxxx>]

On 11.12.19 11:14, Durrant, Paul wrote:
> > -----Original Message-----
> > From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > Sent: 11 December 2019 10:06
> > To: Durrant, Paul <pdurrant@xxxxxxxxxx>
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Juergen
> > Gross <jgross@xxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> > Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > 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.

Juergen

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