linux-kernel - RE: [PATCH 1/4] xenbus: move xenbus_dev

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Message-ID: <bd8a9c19fd944e0faf7a36354db2d495@EX13D32EUC003.ant.amazon.com>
Date:   Mon, 9 Dec 2019 11:55:23 +0000
From:   "Durrant, Paul" <pdurrant@...zon.com>
To:     Jürgen Groß <jgross@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
CC:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: RE: [PATCH 1/4] xenbus: move xenbus_dev_shutdown() into frontend
 code...

> -----Original Message-----
> From: Jürgen Groß <jgross@...e.com>
> Sent: 09 December 2019 11:34
> To: Durrant, Paul <pdurrant@...zon.com>; linux-kernel@...r.kernel.org;
> xen-devel@...ts.xenproject.org
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>; Stefano Stabellini
> <sstabellini@...nel.org>
> Subject: Re: [PATCH 1/4] xenbus: move xenbus_dev_shutdown() into frontend
> code...
> 
> On 05.12.19 15:01, Paul Durrant wrote:
> > ...and make it static
> >
> > xenbus_dev_shutdown() is seemingly intended to cause clean shutdown of
> PV
> > frontends when a guest is rebooted. Indeed the function waits for a
> > conpletion which is only set by a call to xenbus_frontend_closed().
> >
> > This patch removes the shutdown() method from backends and moves
> > xenbus_dev_shutdown() from xenbus_probe.c into xenbus_probe_frontend.c,
> > renaming it appropriately and making it static.
> 
> Is this a good move considering driver domains?

I don't think it can have ever worked properly for driver domains, and with the rest of the patches a backend should be able go away and return unannounced (as long as the domain id is kept... for which patches need to be upstreamed into Xen).

> 
> At least I'd expect the commit message addressing the expected behavior
> with rebooting a driver domain and why this patch isn't making things
> worse.
> 

For a clean reboot I'd expect the toolstack to shut down the protocol before rebooting the driver domain, so the backend shutdown method is moot. And I don't believe re-startable driver domains were something that ever made it into support (because of the non-persistent domid problem). I can add something to the commit comment to that effect if you'd like.

  Paul