From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55820) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YwtZ4-0001JG-5C for qemu-devel@nongnu.org; Mon, 25 May 2015 10:41:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YwtZ3-0003Ov-AP for qemu-devel@nongnu.org; Mon, 25 May 2015 10:41:14 -0400 Sender: Paolo Bonzini Message-ID: <5563347C.10900@redhat.com> Date: Mon, 25 May 2015 16:41:00 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1432266060-22104-1-git-send-email-famz@redhat.com> <1432266060-22104-4-git-send-email-famz@redhat.com> <5563337C.6010009@redhat.com> In-Reply-To: <5563337C.6010009@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v4 3/8] mirror: Do zero write on target if sectors not allocated List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng , qemu-devel@nongnu.org Cc: Stefan Hajnoczi , qemu-stable@nongnu.org, qemu-block@nongnu.org, wangxiaolong@ucloud.cn On 25/05/2015 16:36, Paolo Bonzini wrote: > > > On 22/05/2015 05:40, Fam Zheng wrote: >> + ret = bdrv_get_block_status(source, NULL, sector_num, nb_sectors, &pnum); >> + if (ret < 0 || pnum < nb_sectors || >> + (ret & BDRV_BLOCK_ALLOCATED && !(ret & BDRV_BLOCK_ZERO))) { >> + bdrv_aio_readv(source, sector_num, &op->qiov, nb_sectors, >> + mirror_read_complete, op); >> + } else if (ret & BDRV_BLOCK_ZERO) { >> + bdrv_aio_write_zeroes(s->target, sector_num, op->nb_sectors, >> + s->unmap ? BDRV_REQ_MAY_UNMAP : 0, >> + mirror_write_complete, op); >> + } else { >> + assert(!(ret & BDRV_BLOCK_ALLOCATED)); >> + bdrv_aio_discard(s->target, sector_num, op->nb_sectors, >> + mirror_write_complete, op); >> + } > > This doesn't work if you have a backing file. You want to test > BDRV_BLOCK_DATA, not BDRV_BLOCK_ALLOCATED. > > On the other hand, if BDRV_BLOCK_ALLOCATED is nonzero, you need to > recurse on bs->backing_hd. The logic is very similar to > bdrv_is_allocated_above, but you need to write bdrv_get_block_status_above. Oops, I totally missed the "NULL" in the first line. Still, I think BDRV_BLOCK_DATA is a better check than BDRV_BLOCK_ALLOCATED. Paolo