From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=45567 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OHHNK-0003NK-N5 for qemu-devel@nongnu.org; Wed, 26 May 2010 10:14:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OHHHX-0003pH-UQ for qemu-devel@nongnu.org; Wed, 26 May 2010 10:08:28 -0400 Received: from mail-vw0-f45.google.com ([209.85.212.45]:60476) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OHHHX-0003p8-Rk for qemu-devel@nongnu.org; Wed, 26 May 2010 10:08:27 -0400 Received: by vws6 with SMTP id 6so1022069vws.4 for ; Wed, 26 May 2010 07:08:27 -0700 (PDT) Message-ID: <4BFD2B58.6000503@codemonkey.ws> Date: Wed, 26 May 2010 09:08:24 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive 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> <4BFC0FF6.1080005@suse.de> <20100525210113.GE1402@hall.aurel32.net> <4BFC79E8.1070700@codemonkey.ws> <4BFCDF4D.5020703@redhat.com> <4BFD2542.9090003@codemonkey.ws> <4BFD2A1D.9050903@redhat.com> In-Reply-To: <4BFD2A1D.9050903@redhat.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Alexander Graf , hch@lst.de, qemu-devel@nongnu.org, Aurelien Jarno , Paul Brook On 05/26/2010 09:03 AM, Kevin Wolf wrote: > Am 26.05.2010 15:42, schrieb Anthony Liguori: > >> On 05/26/2010 03:43 AM, Kevin Wolf wrote: >> >>> Am 26.05.2010 03:31, schrieb Anthony Liguori: >>> >>> >>>> On 05/25/2010 04:01 PM, Aurelien Jarno wrote: >>>> >>>> >>>>> I really think this patch can be useful, in my own case when testing >>>>> debian-installer (I already cache=writeback). In short all that is about >>>>> developing and testing, as opposed to run a VM in production, can >>>>> benefit about that. This was one of the original use case of QEMU before >>>>> KVM arrived. >>>>> >>>>> Unless someone can convince me not to do it, I seriously considering >>>>> applying this patch. >>>>> >>>>> >>>>> >>>> There really needs to be an indication in the --help output of what the >>>> ramifications of this option are, in the very least. It should also be >>>> removable via a ./configure option because no sane distribution should >>>> enable this for end users. >>>> >>>> >>> We know better what you stupid user want? >>> >> What percentage of qemu users do you think have actually read qemu-doc.texi? >> > As I said, put the warning in the option name like cache=unsafe or > something even more scary and I'm all for it. > > >> It's not a stretch for someone to have heard that cache options can >> improve performance, and then see cache=volatile in the help output, try >> it, and then start using it because they observe a performance improvement. >> >> That's not being stupid. I think it's a reasonable expectation for a >> user to have that their data is safe. >> > You seem to think that the user is too stupid to allow him to use this > option even if he's perfectly aware what it's doing. It's a useful > option if it's used right. > No, that's not what I said. I'm saying we need to try hard to make a user aware of what they're doing. If it spit out a warning on stdio, I wouldn't think a compile option is needed. Even with help output text, I'm concerned that someone is going to find a bad example on the internet. cache=unsafe addresses the problem although I think it's a bit hokey. > We need to make clear that it's dangerous when it's used in the wrong > cases (for example by naming), but just disabling is not a solution for > that. You don't suggest that "no sane distribution" should ship rm, > because it's dangerous if you use it wrong, do you? > You realize that quite a lot of distributions carry a patch to rm that prevents a user from doing rm -rf /? Regards, Anthony Liguori > Kevin >