From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44986) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XvjZE-0005Lm-2A for qemu-devel@nongnu.org; Tue, 02 Dec 2014 04:16:26 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XvjZ7-000683-TZ for qemu-devel@nongnu.org; Tue, 02 Dec 2014 04:16:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57661) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XvjZ7-00067z-KK for qemu-devel@nongnu.org; Tue, 02 Dec 2014 04:16:13 -0500 Message-ID: <547D8356.1090106@redhat.com> Date: Tue, 02 Dec 2014 10:16:06 +0100 From: Max Reitz MIME-Version: 1.0 References: <1416487488-8423-1-git-send-email-mreitz@redhat.com> <20141126161748.GH3548@noname.str.redhat.com> <877fyf1gbu.fsf@blackfin.pond.sub.org> In-Reply-To: <877fyf1gbu.fsf@blackfin.pond.sub.org> Content-Type: text/plain; charset=iso-8859-15; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 0/3] blockdev: Add read-only option to change-blockdev List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Markus Armbruster , Kevin Wolf Cc: Peter Lieven , qemu-devel@nongnu.org, Stefan Hajnoczi , Luiz Capitulino On 2014-11-28 at 16:43, Markus Armbruster wrote: > Kevin Wolf writes: > >> Am 20.11.2014 um 13:44 hat Max Reitz geschrieben: >>> The 'change' QMP and HMP command allows replacing the medium in drives >>> which support this, e.g. floppy disk drives. For some drives, the medium >>> carries information about whether it can be written to or not (again, >>> floppy drives). Therefore, it should be possible to change the read-only >>> state of block devices when changing the loaded medium. >>> >>> This series adds an optional additional parameter to the 'change' QMP >>> and HMP command which allows changing the read-only state in four ways: >>> >>> - 'retain': Just keep the status as it was before; this is the current >>> behavior and thus this will be the default. >>> - 'ro': Force read-only access >>> - 'rw': Force writable access >>> - 'auto': This opens the new file R/W first, if that fails, the file is >>> opened read-only. >> Not sure if 'auto' is worth implementing (it's a typical HMP default >> action that no QMP client would use, except that it isn't even the >> default for HMP), but the implementation looks correct at least. > QMP eschews magic. I'd prefer to keep 'auto' out. > > HMP can offer it regardless, if it's useful. But I doubt it will be. > Few users will need to control this, and fewer will realize they can by > giving an extra argument. Well, Kevin made the good point of the user generally knowing whether a file should be written to or not. Furthermore, I don't think it would be too hard to use rw, then see that access was denied, and then use ro, manually. Maybe that's even better than auto, somehow. Max > I wish I could tell you to leave change alone because it's a legacy > dungpile. Alas, it's still only a dungpile. I hope we can create a set > of sane media control commands relatively soon now.