From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56826) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZSqmn-00071c-Bo for qemu-devel@nongnu.org; Fri, 21 Aug 2015 14:11:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZSqmi-0004s0-By for qemu-devel@nongnu.org; Fri, 21 Aug 2015 14:11:29 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:36359 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZSqmi-0004qf-0m for qemu-devel@nongnu.org; Fri, 21 Aug 2015 14:11:24 -0400 Message-ID: <55D769C4.4010205@kamp.de> Date: Fri, 21 Aug 2015 20:11:16 +0200 From: Peter Lieven MIME-Version: 1.0 References: <1440143355-2918-1-git-send-email-pl@kamp.de> <55D755F6.2@redhat.com> In-Reply-To: <55D755F6.2@redhat.com> Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] block/nfs: cache allocated filesize for read-only files List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz , qemu-devel@nongnu.org, qemu-block@nongnu.org Cc: kwolf@redhat.com, jcody@redhat.com Am 21.08.2015 um 18:46 schrieb Max Reitz: > On 2015-08-21 at 00:49, 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 >> --- >> block/nfs.c | 6 ++++++ >> 1 file changed, 6 insertions(+) > > First, I don't like the idea of this patch very much, but since I've never used qemu's native NFS client, it's not up to me to decide whether it's worth it. I am trying to solve that a stale NFS Server with a CDROM ISO on it can hang Qemus main loop. One of the things that happens is that you query "info block" in hmp or "query-block" via QMP and indirectly call bdrv_get_allocated_file_size and bang, Qemu hangs. Also I don't know if its worth to issue an RPC call for each executing of info block. > > When it comes to breaking this, what comes to mind first is some external program opening the image read-write outside of qemu and writing to it. Maybe that's a case we generally don't want, but maybe that's something some people do on purpose, knowing what they're doing (with raw images), you never know. I would consider this bad behaviour. However, allocated file size shouldn't matter for raw images. If you resize the image from external you have to call bdrv_truncate anyway to make Qemu aware of that change. > > Other than that, there's reopening. As far as I'm aware, qemu can reopen a R/W image read-only, and if that happens, st_blocks may be stale. Thats a valid point. But it can be solved be implementing .bdrv_reopen_prepare and update st_blocks there. Thanks for you thoughts, Peter