@@ -1171,7 +1171,7 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
* modifying the image file. This is critical for zero-copy guest I/O
* where anything might happen inside guest memory.
*/
- void *bounce_buffer;
+ void *bounce_buffer = NULL;
BlockDriver *drv = bs->drv;
int64_t cluster_offset;
@@ -1206,14 +1206,6 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
trace_bdrv_co_do_copy_on_readv(bs, offset, bytes,
cluster_offset, cluster_bytes);
- bounce_buffer = qemu_try_blockalign(bs,
- MIN(MIN(max_transfer, cluster_bytes),
- MAX_BOUNCE_BUFFER));
- if (bounce_buffer == NULL) {
- ret = -ENOMEM;
- goto err;
- }
-
while (cluster_bytes) {
int64_t pnum;
@@ -1240,6 +1232,17 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
/* Must copy-on-read; use the bounce buffer */
pnum = MIN(pnum, MAX_BOUNCE_BUFFER);
+ if (!bounce_buffer) {
+ int64_t max_we_need = MAX(pnum, cluster_bytes - pnum);
+ int64_t max_allowed = MIN(max_transfer, MAX_BOUNCE_BUFFER);
+ int64_t bounce_buffer_len = MIN(max_we_need, max_allowed);
+
+ bounce_buffer = qemu_try_blockalign(bs, bounce_buffer_len);
+ if (!bounce_buffer) {
+ ret = -ENOMEM;
+ goto err;
+ }
+ }
qemu_iovec_init_buf(&local_qiov, bounce_buffer, pnum);
ret = bdrv_driver_preadv(bs, cluster_offset, pnum,
Allocate bounce_buffer only if it is really needed. Also, sub-optimize allocation size (why not?). Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> --- block/io.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-)