From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58098) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1byVG5-0003TN-Vf for qemu-devel@nongnu.org; Sun, 23 Oct 2016 22:45:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1byVG5-0004ST-1f for qemu-devel@nongnu.org; Sun, 23 Oct 2016 22:45:05 -0400 References: <1476971860-20860-1-git-send-email-zhang.zhanghailiang@huawei.com> <1476971860-20860-8-git-send-email-zhang.zhanghailiang@huawei.com> <316427bf-36f6-7945-e143-8d51efc78978@redhat.com> From: Hailiang Zhang Message-ID: <580D7587.1070400@huawei.com> Date: Mon, 24 Oct 2016 10:44:23 +0800 MIME-Version: 1.0 In-Reply-To: <316427bf-36f6-7945-e143-8d51efc78978@redhat.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH RFC 7/7] nbd/replication: implement .bdrv_get_info() for nbd and replication driver List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake , qemu-devel@nongnu.org, qemu-block@nongnu.org Cc: kwolf@redhat.com, xiecl.fnst@cn.fujitsu.com, mreitz@redhat.com, stefanha@redhat.com, pbonzini@redhat.com Hi, On 2016/10/20 23:34, Eric Blake wrote: > On 10/20/2016 08:57 AM, zhanghailiang wrote: >> Without this callback, there will be an error reports in the primary side: >> "qemu-system-x86_64: Couldn't determine the cluster size of the target image, >> which has no backing file: Operation not supported >> Aborting, since this may create an unusable destination image" >> >> For nbd driver, it doesn't have cluster size, so here we return >> a fake value for it. >> >> Signed-off-by: zhanghailiang >> Signed-off-by: Wen Congyang >> --- >> block/nbd.c | 12 ++++++++++++ >> block/replication.c | 6 ++++++ >> 2 files changed, 18 insertions(+) >> >> diff --git a/block/nbd.c b/block/nbd.c >> index 6bc06d6..96d7023 100644 >> --- a/block/nbd.c >> +++ b/block/nbd.c >> @@ -40,6 +40,8 @@ >> >> #define EN_OPTSTR ":exportname=" >> >> +#define NBD_FAKE_CLUSTER_SIZE 512 > > Why 512? NBD allows byte-addressable operations (even if it is more > efficient on aligned I/O); and I've been working hard to convert things > to the point that NBD does not enforce alignment on other layers. > Wouldn't 1 be better? > Yes, that makes no difference for block replication driver. :) >> +static int nbd_get_info(BlockDriverState *bs, BlockDriverInfo *bdi) >> +{ >> + bdi->cluster_size = NBD_FAKE_CLUSTER_SIZE; > > I also have patches written (but waiting for NBD write zeroes support to > be reviewed first) that add support for the experimental NBD block info, > that lets a server advertise actual sizes to the client rather than > having to guess. Here's the last time I posted a preview of it: > > https://lists.gnu.org/archive/html/qemu-devel/2016-04/msg03567.html > > It would be nice to use that instead of just faking things. > That's great, that's what we really want, here it is just a temporary solution, I'll drop this patch after you nbd patch been merged. Thanks, Hailiang