From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1755463AbcKOOiu (ORCPT <rfc822;w@1wt.eu>);
        Tue, 15 Nov 2016 09:38:50 -0500
Received: from mx1.redhat.com ([209.132.183.28]:57878 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1753124AbcKOOis (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 15 Nov 2016 09:38:48 -0500
Date: Tue, 15 Nov 2016 16:38:45 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org,
        qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Anthony Liguori <aliguori@amazon.com>,
        Anton Vorontsov <anton@enomsg.org>, Colin Cross <ccross@android.com>,
        Kees Cook <keescook@chromium.org>, Tony Luck <tony.luck@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@kernel.org>,
        Minchan Kim <minchan@kernel.org>,
        "Daniel P . Berrange" <berrange@redhat.com>
Subject: Re: [PATCH 2/3] qemu: Implement virtio-pstore device
Message-ID: <20161115163735-mutt-send-email-mst@kernel.org>
References: <20160820080744.10344-1-namhyung@kernel.org>
 <20160820080744.10344-3-namhyung@kernel.org>
 <20160913155710.3q6yj6yqdyozemul@redhat.com>
 <20160916100547.GC2474@danjae.aot.lge.com>
 <20161111004710-mutt-send-email-mst@kernel.org>
 <20161115062336.GA16821@danjae.aot.lge.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20161115062336.GA16821@danjae.aot.lge.com>
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Tue, 15 Nov 2016 14:38:48 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Nov 15, 2016 at 03:23:36PM +0900, Namhyung Kim wrote:
> On Fri, Nov 11, 2016 at 12:50:03AM +0200, Michael S. Tsirkin wrote:
> > On Fri, Sep 16, 2016 at 07:05:47PM +0900, Namhyung Kim wrote:
> > > On Tue, Sep 13, 2016 at 06:57:10PM +0300, Michael S. Tsirkin wrote:
> > > > On Sat, Aug 20, 2016 at 05:07:43PM +0900, Namhyung Kim wrote:
> > > > > +
> > > > > +/* the index should match to the type value */
> > > > > +static const char *virtio_pstore_file_prefix[] = {
> > > > > +    "unknown-",		/* VIRTIO_PSTORE_TYPE_UNKNOWN */
> > > > 
> > > > Is there value in treating everything unexpected as "unknown"
> > > > and rotating them as if they were logs?
> > > > It might be better to treat everything that's not known
> > > > as guest error.
> > > 
> > > I was thinking about the version mismatch between the kernel and qemu.
> > > I'd like to make the device can deal with a new kernel version which
> > > might implement a new pstore message type.  It will be saved as
> > > unknown but the kernel can read it properly later.
> > 
> > Well it'll have a different prefix. E.g. if kernel has
> > two different types they will end up in the same
> > file, hardly what was wanted.
> 
> Right, I think it needs to add 'type' info to the filename for unknown
> type.
> 
> Thanks,
> Namhyung

And that opens all kind of resource management issues as guest
might be able to open a ton of these unexpected types.
So don't try to predict the future, if you add a new type
you add a feature flag. Ignore or error on things you can
not handle.

-- 
MST