From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:53461) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Rvpq9-00012Z-6q for qemu-devel@nongnu.org; Fri, 10 Feb 2012 07:44:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Rvpq3-0006Bv-Ix for qemu-devel@nongnu.org; Fri, 10 Feb 2012 07:44:37 -0500 Received: from mx1.redhat.com ([209.132.183.28]:23255) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Rvpq3-0006BG-7x for qemu-devel@nongnu.org; Fri, 10 Feb 2012 07:44:31 -0500 From: Kevin Wolf Date: Fri, 10 Feb 2012 13:47:32 +0100 Message-Id: <1328878064-4907-4-git-send-email-kwolf@redhat.com> In-Reply-To: <1328878064-4907-1-git-send-email-kwolf@redhat.com> References: <1328878064-4907-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PATCH 03/15] block: perform zero-detection during copy-on-read List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: anthony@codemonkey.ws Cc: kwolf@redhat.com, qemu-devel@nongnu.org From: Stefan Hajnoczi Copy-on-Read populates the image file with data read from a backing image. In order to avoid bloating the image file when all zeroes are read we should scan the buffer and perform an optimized zero write operation. Signed-off-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- block.c | 14 +++++++++++--- 1 files changed, 11 insertions(+), 3 deletions(-) diff --git a/block.c b/block.c index c9fa5c1..ae297bb 100644 --- a/block.c +++ b/block.c @@ -1517,6 +1517,7 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs, */ void *bounce_buffer; + BlockDriver *drv = bs->drv; struct iovec iov; QEMUIOVector bounce_qiov; int64_t cluster_sector_num; @@ -1537,14 +1538,21 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BlockDriverState *bs, iov.iov_base = bounce_buffer = qemu_blockalign(bs, iov.iov_len); qemu_iovec_init_external(&bounce_qiov, &iov, 1); - ret = bs->drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors, - &bounce_qiov); + ret = drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors, + &bounce_qiov); if (ret < 0) { goto err; } - ret = bs->drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors, + if (drv->bdrv_co_write_zeroes && + buffer_is_zero(bounce_buffer, iov.iov_len)) { + ret = drv->bdrv_co_write_zeroes(bs, cluster_sector_num, + cluster_nb_sectors); + } else { + ret = drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors, &bounce_qiov); + } + if (ret < 0) { /* It might be okay to ignore write errors for guest requests. If this * is a deliberate copy-on-read then we don't want to ignore the error. -- 1.7.6.5