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>
---
qemu-img.c | 27 +++++++++++++++++++++++++--
1 file changed, 25 insertions(+), 2 deletions(-)
diff --git a/qemu-img.c b/qemu-img.c
index 06264d9..ad1df5f 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1451,6 +1451,22 @@ static void convert_select_part(ImgConvertState *s,
int64_t sector_num)
}
}
+static int64_t get_backing_status(BlockDriverState *bs,
+ int64_t sector_num,
+ int nb_sectors, int *pnum)
+{
+ int64_t ret;
+ BlockDriverState *file;
+ ret = bdrv_get_block_status(bs, sector_num, nb_sectors, pnum, &file);
+ if (!(ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO))) {
+ if (bs->backing) {
+ ret = get_backing_status(bs->backing->bs, sector_num,
+ nb_sectors, pnum);
+ }
+ }
+ return ret;
+}
+
static int convert_iteration_sectors(ImgConvertState *s, int64_t sector_num)
{
int64_t ret;
@@ -1477,10 +1493,17 @@ 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 = get_backing_status(blk_bs(s->src[s->src_cur]),
+ sector_num - s->src_cur_offset,
+ n, &n);
+ if (ret & BDRV_BLOCK_ZERO) {
+ s->status = BLK_ZERO;
+ } else {
+ s->status = BLK_DATA;
+ }
} else {
s->status = BLK_BACKING_FILE;
}
--
2.5.0
