From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Jackson <Ian.Jackson@eu.citrix.com>
Subject: Re: [PATCH v4 4/4] libxl: fix cd-eject
Date: Tue, 16 Feb 2016 17:58:16 +0000
Message-ID: <22211.25400.584104.350999@mariner.uk.xensource.com>
References: <1455644269-40358-1-git-send-email-roger.pau@citrix.com>
	<1455644269-40358-5-git-send-email-roger.pau@citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Received: from mail6.bemta14.messagelabs.com ([193.109.254.103])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <prvs=847df0986=Ian.Jackson@citrix.com>)
	id 1aVjtE-000277-Lp
	for xen-devel@lists.xenproject.org; Tue, 16 Feb 2016 17:58:20 +0000
In-Reply-To: <1455644269-40358-5-git-send-email-roger.pau@citrix.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org, Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Alex Braunegg <alex.braunegg@gmail.com>
List-Id: xen-devel@lists.xenproject.org

Roger Pau Monne writes ("[PATCH v4 4/4] libxl: fix cd-eject"):
> Current libxl__device_disk_set_backend implementation tried to guess the
> backend of devices with format LIBXL_DISK_FORMAT_EMPTY, which is of course
> doomed to fail since the disk is empty. Instead just return early from the
> function if an empty disk is detected.
> 
> This fixes cd ejection.

DYK when this was broken ?  Or, to put it another way, how did this
ever work ?

...looking at the code...

AFAICT disk_try_backend should succeed for both LIBXL_DISK_BACKEND_PHY
and LIBXL_DISK_BACKEND_QDISK.  So even before your patch:

>          }
> -        memset(&a.stab, 0, sizeof(a.stab));
> +        /* Disk is empty, so it's useless to try to guess the backend type. */
> +        return 0;
>      } else if ((disk->backend == LIBXL_DISK_BACKEND_UNKNOWN ||

libxl__device_disk_set_backend should work.

Worse, this change seems to leave disk->backend unset on return from
libxl__device_disk_set_backend, which seems quite wrong to me.

Ian.