From: Ren Kimura <rkx1209...@gmail.com>
When converting images, check the block status of its backing file chain
to avoid needlessly reading zeros.
Signed-off-by: Ren Kimura <rkx1209...@gmail.com>
Message-id: 1461773098-20356-1-git-send-email-rkx1209...@gmail.com
Signed-off-by: Max Reitz <mre...@redhat.com>
---
qemu-img.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/qemu-img.c b/qemu-img.c
index 491a460..4792366 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;
}
--
1.8.3.1
