From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=42974 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1ObhJI-000617-Hk for qemu-devel@nongnu.org; Wed, 21 Jul 2010 17:58:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1ObhJH-0004aj-30 for qemu-devel@nongnu.org; Wed, 21 Jul 2010 17:58:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58185) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1ObhJG-0004aX-SR for qemu-devel@nongnu.org; Wed, 21 Jul 2010 17:58:39 -0400 Date: Wed, 21 Jul 2010 22:58:33 +0100 From: "Daniel P. Berrange" Subject: Re: [Qemu-devel] [PATCH] move 'unsafe' to end of caching modes in help Message-ID: <20100721215833.GC28871@redhat.com> References: <4C4704FC020000480009AB6E@sinclair.provo.novell.com> <4C475EC0.2000805@codemonkey.ws> <20100721213238.GB28871@redhat.com> <4C476A8A.6000707@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C476A8A.6000707@codemonkey.ws> Reply-To: "Daniel P. Berrange" List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: qemu-devel@nongnu.org, Bruce Rogers On Wed, Jul 21, 2010 at 04:45:46PM -0500, Anthony Liguori wrote: > On 07/21/2010 04:32 PM, Daniel P. Berrange wrote: > >On Wed, Jul 21, 2010 at 03:55:28PM -0500, Anthony Liguori wrote: > > > >>On 07/21/2010 03:32 PM, Bruce Rogers wrote: > >> > >>>Libvirt parses qemu help output to determine qemu features. In particular > >>> it probes for the following: "cache=writethrough|writeback|none". The > >>> addition of the unsafe cache mode was inserted within this string, as > >>> opposed to being added to the end, which impacted libvirt's probe. > >>> Unbreak libvirt by keeping the existing cache modes intact and add > >>> unsafe to the end. > >>> > >>>This problem only manifests itself if a caching mode is explicitly > >>>specified in the libvirt xml, in which case older syntax for caching is > >>>passed to qemu, which it no longer understands. > >>> > >>>Signed-off-by: Bruce Rogers > >>> > >>> > >>Errr, libvirt is still doing this? > >> > >>This comes up frequently and it's a real PITA. Help text is not a > >>feature probing interface. This is a libvirt bug and it needs to be > >>fixed in libvirt > >> > >Of course, there is no viable alternative yet. > > Yes there is. Use the version number. The version number is not suitable, because features can be removed at compile time and/or added via patch backports. The only reliable way is to query the QEMU binary to ask it what it actually supports. Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://deltacloud.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|