From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=53432 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OE6bc-0007y4-2d for qemu-devel@nongnu.org; Mon, 17 May 2010 16:08:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OE6bR-0007Nj-Hu for qemu-devel@nongnu.org; Mon, 17 May 2010 16:08:03 -0400 Received: from mail2.shareable.org ([80.68.89.115]:50114) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OE6bR-0007Ne-1E for qemu-devel@nongnu.org; Mon, 17 May 2010 16:07:53 -0400 Date: Mon, 17 May 2010 21:07:43 +0100 From: Jamie Lokier Subject: Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive Message-ID: <20100517200743.GI20356@shareable.org> References: <1274091292-4812-1-git-send-email-agraf@suse.de> <4BF14CE9.5040907@suse.de> <4BF15DC8.8080104@codemonkey.ws> <201005171723.15675.paul@codesourcery.com> <4BF16E22.6090400@codemonkey.ws> <498275A3-F2DA-4C59-B8DF-302121442DE0@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <498275A3-F2DA-4C59-B8DF-302121442DE0@suse.de> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: kwolf@redhat.com, qemu-devel@nongnu.org, hch@lst.de, Paul Brook Alexander Graf wrote: > > On 17.05.2010, at 18:26, Anthony Liguori wrote: > > > On 05/17/2010 11:23 AM, Paul Brook wrote: > >>>> I don't see a difference between the results. Apparently the barrier > >>>> option doesn't change a thing. > >>>> > >>> Ok. I don't like it, but I can see how it's compelling. I'd like to > >>> see the documentation improved though. I also think a warning printed > >>> on stdio about the safety of the option would be appropriate. > >>> > >> I disagree with this last bit. > >> > >> Errors should be issued if the user did something wrong. > >> Warnings should be issued if qemu did (or will soon do) something other than > >> what the user requested, or otherwise made questionable decisions on the > >> user's behalf. > >> > >> In this case we're doing exactly what the user requested. The only plausible > >> failure case is where a user is blindly trying options that they clearly don't > >> understand or read the documentation for. I have zero sympathy for complaints > >> like "Someone on the Internet told me to use --breakme, and broke thinks". > >> > > > > I see it as the equivalent to the Taint bit in Linux. I want to make it clear to users up front that if you use this option, and you have data loss issues, don't complain. > > > > Just putting something in qemu-doc.texi is not enough IMHO. Few people actually read it. > > But that's why it's no default and also called "volatile". If you prefer, we can call it cache=destroys_your_image. With that semantic, a future iteration of cache=volatile could even avoid writing to the backing file at all, if that's yet faster. I wonder if that would be faster. Anyone fancy doing a hack with the whole guest image as a big malloc inside qemu? I don't have enough RAM :-) -- Jamie