Re: [Qemu-devel] [PATCH v5] qemu-img: check block status of backing file when converting.

[Max Reitz]

On 27.04.2016 18:04, Ren Kimura wrote:
> When converting images, check the block status of its backing file chain
> to avoid needlessly reading zeros.
> 
> Signed-off-by: Ren Kimura 
> ---
>  qemu-img.c | 15 +--
>  1 file changed, 13 insertions(+), 2 deletions(-)

Thank you, I applied the patch to my block-next tree for inclusion into
qemu after the 2.6 release:

https://github.com/XanClic/qemu/commits/block-next

Max



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[Qemu-devel] [PATCH v5] qemu-img: check block status of backing file when converting.

[Ren Kimura]

When converting images, check the block status of its backing file chain
to avoid needlessly reading zeros.

Signed-off-by: Ren Kimura 
---
 qemu-img.c | 15 +--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 1697762..cb72f14 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1478,10 +1478,21 @@ 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, , );
+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;
 }
-- 
2.5.0