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block: limited request size in write zeroes unsupported path 

If bs->bl.max_write_zeroes is large and we end up in the unsupported
path we might allocate a lot of memory for the iovector and/or even
generate an oversized requests.

Fix this by limiting the request by the minimum of the reported
maximum transfer size or 16MB (32768 sectors).

Reported-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Message-id: 1420457389-16332-1-git-send-email-pl@kamp.de
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
master
Peter Lieven 2015-01-05 12:29:49 +01:00 committed by Stefan Hajnoczi
parent 51a2219bdc
commit 095e4fa4b5
1 changed files with 4 additions and 1 deletions
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5
block.c
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@ -3244,6 +3244,9 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
if (ret == -ENOTSUP) {
/* Fall back to bounce buffer if write zeroes is unsupported */
int max_xfer_len = MIN_NON_ZERO(bs->bl.max_transfer_length,
MAX_WRITE_ZEROES_DEFAULT);
num = MIN(num, max_xfer_len);
iov.iov_len = num * BDRV_SECTOR_SIZE;
if (iov.iov_base == NULL) {
iov.iov_base = qemu_try_blockalign(bs, num * BDRV_SECTOR_SIZE);
@ -3260,7 +3263,7 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
/* Keep bounce buffer around if it is big enough for all
* all future requests.
*/
if (num < max_write_zeroes) {
if (num < max_xfer_len) {
qemu_vfree(iov.iov_base);
iov.iov_base = NULL;
}