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

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Message-ID: <86a7d140501047028c49736c43fe547c@EX13D32EUC003.ant.amazon.com>
Date:   Wed, 11 Dec 2019 10:14:59 +0000
From:   "Durrant, Paul" <pdurrant@...zon.com>
To:     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>,
        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

> -----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 :-)

  Paul