From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55311) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YIdqR-0005kL-QO for qemu-devel@nongnu.org; Tue, 03 Feb 2015 08:48:48 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YIdqN-0005sz-0S for qemu-devel@nongnu.org; Tue, 03 Feb 2015 08:48:47 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51595) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YIdqM-0005sp-Oa for qemu-devel@nongnu.org; Tue, 03 Feb 2015 08:48:42 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t13Dmf3I025747 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Tue, 3 Feb 2015 08:48:42 -0500 Message-ID: <54D0D1B8.4000500@redhat.com> Date: Tue, 03 Feb 2015 08:48:40 -0500 From: Max Reitz MIME-Version: 1.0 References: <1411588107-4275-1-git-send-email-mreitz@redhat.com> <20150203093205.GB4488@noname.redhat.com> In-Reply-To: <20150203093205.GB4488@noname.redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 0/4] block: Drop BDS.filename List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org, Stefan Hajnoczi On 2015-02-03 at 04:32, Kevin Wolf wrote: > Am 24.09.2014 um 21:48 hat Max Reitz geschrieben: >> The BDS filename field is generally only used when opening disk images >> or emitting error or warning messages, the only exception to this rule >> is the map command of qemu-img. However, using exact_filename there >> instead should not be a problem. Therefore, we can drop the filename >> field from the BlockDriverState and use a function instead which builds >> the filename from scratch when called. >> >> This is slower than reading a static char array but the problem of that >> static array is that it may become obsolete due to changes in any >> BlockDriverState or in the BDS graph. Using a function which rebuilds >> the filename every time it is called resolves this problem. >> >> The disadvantage of worse performance is negligible, on the other hand. >> After patch 2 of this series, which replaces some queries of >> BDS.filename by reads from somewhere else (mostly BDS.exact_filename), >> the filename field is only used when a disk image is opened or some >> message should be emitted, both of which cases do not suffer from the >> performance hit. > Surprisingly (or not), this one needs rebasing. Well... > I tried it and it doesn't look too hard, but it's a little bit more than > what I'm comfortable with doing while applying a series. I admire your courage, but I'm not sure whether this series is ready for being applied at all. First we (or I) will have to look into how users like libvirt which identify a BDS based on the filename can break from applying this series. Max