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authorStefan Hajnoczi <stefanha@linux.vnet.ibm.com>2012-02-07 13:27:26 +0000
committerKevin Wolf <kwolf@redhat.com>2012-02-09 16:17:50 +0100
commit79c053bde9fa40595670ae274d047da07f1df88c (patch)
treedc859b1ca2cb3345bdc665fca11f9c0cf4b35cf5
parentf08f2ddae078e8a7683f8b16da8e0cc3029c7b89 (diff)
block: perform zero-detection during copy-on-read
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 <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
-rw-r--r--block.c14
1 files changed, 11 insertions, 3 deletions
diff --git a/block.c b/block.c
index c9fa5c17f..ae297bb84 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.