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

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Date:   Wed, 11 Dec 2019 13:29:03 +0000
From:   "Durrant, Paul" <pdurrant@...zon.com>
To:     Jürgen Groß <jgross@...e.com>,
        Roger Pau Monné <roger.pau@...rix.com>
CC:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Stefano Stabellini" <sstabellini@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: RE: [Xen-devel] [PATCH v2 2/4] xenbus: limit when state is forced to
 closed

> -----Original Message-----
> From: Jürgen Groß <jgross@...e.com>
> Sent: 11 December 2019 10:21
> To: Durrant, Paul <pdurrant@...zon.com>; Roger Pau Monné
> <roger.pau@...rix.com>
> Cc: xen-devel@...ts.xenproject.org; linux-kernel@...r.kernel.org; Stefano
> Stabellini <sstabellini@...nel.org>; Boris Ostrovsky
> <boris.ostrovsky@...cle.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@...rix.com>
> >> Sent: 11 December 2019 10:06
> >> To: Durrant, Paul <pdurrant@...zon.com>
> >> Cc: xen-devel@...ts.xenproject.org; linux-kernel@...r.kernel.org;
> Juergen
> >> Gross <jgross@...e.com>; Stefano Stabellini <sstabellini@...nel.org>;
> >> Boris Ostrovsky <boris.ostrovsky@...cle.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