From 263a6f4c3aa9b6cd9f58d1368b318d948156a4e8 Mon Sep 17 00:00:00 2001 From: Ren Kimura Date: Thu, 28 Apr 2016 01:04:58 +0900 Subject: [PATCH] qemu-img: check block status of backing file when converting. When converting images, check the block status of its backing file chain to avoid needlessly reading zeros. Signed-off-by: Ren Kimura Message-id: 1461773098-20356-1-git-send-email-rkx1209dev@gmail.com Signed-off-by: Max Reitz --- qemu-img.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/qemu-img.c b/qemu-img.c index 491a460ecf..47923663be 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -1475,10 +1475,21 @@ static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num) } else if (!s->target_has_backing) { /* Without a target backing file we must copy over the contents of * the backing file as well. */ - /* TODO Check block status of the backing file chain to avoid + /* Check block status of the backing file chain to avoid * needlessly reading zeroes and limiting the iteration to the * buffer size */ - s->status = BLK_DATA; + ret = bdrv_get_block_status_above(blk_bs(s->src[s->src_cur]), NULL, + sector_num - s->src_cur_offset, + n, &n, &file); + if (ret < 0) { + return ret; + } + + if (ret & BDRV_BLOCK_ZERO) { + s->status = BLK_ZERO; + } else { + s->status = BLK_DATA; + } } else { s->status = BLK_BACKING_FILE; }