Right now, bdrv_co_do_write_zeroes will only try to align the
beginning of the request. However, it is simpler for many
formats to expect the block layer to separate both the head *and*
the tail. This makes sure that the format's bdrv_co_write_zeroes
function will be called with aligned sector_num and nb_sectors for
the bulk of the request.
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
block.c | 30 +++++++++++++++---------------
1 file changed, 15 insertions(+), 15 deletions(-)
diff --git a/block.c b/block.c
index 4897649..567d669 100644
--- a/block.c
+++ b/block.c
@@ -2761,14 +2761,19 @@ static int coroutine_fn
bdrv_co_do_write_zeroes(BlockDriverState *bs,
while (nb_sectors > 0 && !ret) {
int num = nb_sectors;
- /* align request */
- if (bs->bl.write_zeroes_alignment &&
- num >= bs->bl.write_zeroes_alignment &&
- sector_num % bs->bl.write_zeroes_alignment) {
- if (num > bs->bl.write_zeroes_alignment) {
+ /* Align request. Block drivers can expect the "bulk" of the request
+ * to be aligned.
+ */
+ if (bs->bl.write_zeroes_alignment
+ && num > bs->bl.write_zeroes_alignment) {
+ if (sector_num % bs->bl.write_zeroes_alignment != 0) {
+ /* Make a small request up to the first aligned sector. */
num = bs->bl.write_zeroes_alignment;
+ num -= sector_num % bs->bl.write_zeroes_alignment;
+ } else if (num >= bs->bl.write_zeroes_alignment) {
+ /* Shorten the request to the last aligned sector. */
+ num -= (sector_num + num) % bs->bl.write_zeroes_alignment;
}
- num -= sector_num % bs->bl.write_zeroes_alignment;
}
/* limit request size */
@@ -2785,24 +2790,27 @@ static int coroutine_fn
bdrv_co_do_write_zeroes(BlockDriverState *bs,
if (ret == -ENOTSUP) {
/* Fall back to bounce buffer if write zeroes is unsupported */
iov.iov_len = num * BDRV_SECTOR_SIZE;
if (iov.iov_base == NULL) {
- /* allocate bounce buffer only once and ensure that it
- * is big enough for this and all future requests.
- */
- size_t bufsize = num <= nb_sectors ? num : max_write_zeroes;
- iov.iov_base = qemu_blockalign(bs, bufsize * BDRV_SECTOR_SIZE);
- memset(iov.iov_base, 0, bufsize * BDRV_SECTOR_SIZE);
+ iov.iov_base = qemu_blockalign(bs, num * BDRV_SECTOR_SIZE);
+ memset(iov.iov_base, 0, num * BDRV_SECTOR_SIZE);
}
qemu_iovec_init_external(&qiov, &iov, 1);
ret = drv->bdrv_co_writev(bs, sector_num, num, &qiov);
+ if (num <= max_write_zeroes) {
+ /* Allocate bounce buffer only once if it is
+ * big enough for this and all future requests.
+ */
+ qemu_vfree(iov.iov_base);
+ iov.iov_base = NULL;
+ }
}
sector_num += num;
nb_sectors -= num;
}
qemu_vfree(iov.iov_base);
return ret;
}
--
1.8.4.2
