From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51475) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZUcfg-00042Y-HP for qemu-devel@nongnu.org; Wed, 26 Aug 2015 11:31:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZUcfc-0006hw-Go for qemu-devel@nongnu.org; Wed, 26 Aug 2015 11:31:28 -0400 Date: Wed, 26 Aug 2015 11:31:17 -0400 From: Jeff Cody Message-ID: <20150826153117.GH11016@localhost.localdomain> References: <1440403565-27432-1-git-send-email-pl@kamp.de> <55DB64CC.2040207@redhat.com> <55DB71BD.3080402@kamp.de> <55DB7ADC.1010109@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55DB7ADC.1010109@redhat.com> Subject: Re: [Qemu-devel] [PATCHv2] block/nfs: cache allocated filesize for read-only files List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz Cc: kwolf@redhat.com, Peter Lieven , qemu-devel@nongnu.org, qemu-block@nongnu.org On Mon, Aug 24, 2015 at 10:13:16PM +0200, Max Reitz wrote: > On 24.08.2015 21:34, Peter Lieven wrote: > > Am 24.08.2015 um 20:39 schrieb Max Reitz: > >> On 24.08.2015 10:06, Peter Lieven wrote: > >>> If the file is readonly its not expected to grow so > >>> save the blocking call to nfs_fstat_async and use > >>> the value saved at connection time. Also important > >>> the monitor (and thus the main loop) will not hang > >>> if block device info is queried and the NFS share > >>> is unresponsive. > >>> > >>> Signed-off-by: Peter Lieven > >>> --- > >>> v1->v2: update cache on reopen_prepare [Max] > >>> > >>> block/nfs.c | 35 +++++++++++++++++++++++++++++++++++ > >>> 1 file changed, 35 insertions(+) > >> Reviewed-by: Max Reitz > >> > >> I hope you're ready for the "Stale actual-size value with > >> cache=direct,read-only=on,format=raw files on NFS" reports. :-) > > actually a good point, maybe the cache should only be used if > > > > !(bs->open_flags & BDRV_O_NOCACHE) > > Good enough a point to fix it? ;-) > > Max > It seems more inline with expected behavior, to add the cache checking in before using the size cache. Would you be opposed to a v3 with this check added in? One other concern I have is similar to a concern Max raised earlier - about an external program modifying the raw image, while QEMU has it opened r/o. In particular, I wonder about an NFS server making an image either sparse / non-sparse. If it was exported read-only, it may be a valid assumption that this could be done safely, as it would not change the reported file size or contents, just the allocated size on disk.