From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NLGDp-0005wh-9E for qemu-devel@nongnu.org; Thu, 17 Dec 2009 08:16:49 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NLGDj-0005mY-So for qemu-devel@nongnu.org; Thu, 17 Dec 2009 08:16:47 -0500 Received: from [199.232.76.173] (port=40117 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NLGDj-0005mO-Iu for qemu-devel@nongnu.org; Thu, 17 Dec 2009 08:16:43 -0500 Received: from mail2.shareable.org ([80.68.89.115]:36868) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1NLGDi-000407-4y for qemu-devel@nongnu.org; Thu, 17 Dec 2009 08:16:43 -0500 Date: Thu, 17 Dec 2009 13:16:35 +0000 From: Jamie Lokier Subject: Re: [Qemu-devel] [PATCH] A different way to ask for readonly drive Message-ID: <20091217131635.GA24967@shareable.org> References: <4B263F0B.90408@redhat.com> <4B265F7D.1010109@mail.berlios.de> <20091215184501.GB21298@shareable.org> <20091217105004.GA17205@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091217105004.GA17205@lst.de> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: Naphtali Sprei , qemu-devel@nongnu.org Christoph Hellwig wrote: > On Tue, Dec 15, 2009 at 06:45:01PM +0000, Jamie Lokier wrote: > > access=rw > > access=ro > > access=auto (default) > > Yes, that sounds like the least clumsy one. I still think the current > implementation is a very bad default, though. Without agreeing or disagreeing over whether it's a bad default :), a usability problem occurs with the current implementation when you deliberately "chmod 444" an image to have high confidence that it's opened read only: When running as root, file permissions are ignored (except sometimes on NFS). For that reason I use "chattr +i" on all my read-only image files, to really make sure that no qemu invocation mistake could accidentally corrupt valuable images. That works, but it's not very convenient. If the "auto" method is kept, I think it would be an improvement if it checks the file permission itself, and does not even try to open a file O_RDWR if there are no writable permission bits - so that "chmod 444" has the same "open as read only" effect when qemu is invoked as root. -- Jamie