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block: make bdrv_co_do_write_zeroes stricter in producing aligned requests

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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 <pbonzini@redhat.com>
Reviewed-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Paolo Bonzini 2013-11-22 13:39:48 +01:00 committed by Stefan Hajnoczi
parent 7ce21016b6
commit b8d71c09f3
1 changed files with 23 additions and 12 deletions
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35
block.c
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@ -2771,14 +2771,21 @@ 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 ((sector_num + num) % bs->bl.write_zeroes_alignment != 0) {
/* Shorten the request to the last aligned sector. num cannot
* underflow because num > bs->bl.write_zeroes_alignment.
*/
num -= (sector_num + num) % bs->bl.write_zeroes_alignment;
}
num -= sector_num % bs->bl.write_zeroes_alignment;
}
/* limit request size */
@ -2796,16 +2803,20 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
/* 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);
/* Keep bounce buffer around if it is big enough for all
* all future requests.
*/
if (num < max_write_zeroes) {
qemu_vfree(iov.iov_base);
iov.iov_base = NULL;
}
}
sector_num += num;