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block: honour BlockLimits in bdrv_co_do_write_zeroes

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Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Peter Lieven 2013-10-24 12:06:58 +02:00 committed by Kevin Wolf
parent 04f19e4d2d
commit c31cb70728
1 changed files with 50 additions and 17 deletions
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67
block.c
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@ -2711,33 +2711,66 @@ int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
BDRV_REQ_COPY_ON_READ);
}
/* if no limit is specified in the BlockLimits use a default
* of 32768 512-byte sectors (16 MiB) per request.
*/
#define MAX_WRITE_ZEROES_DEFAULT 32768
static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
int64_t sector_num, int nb_sectors, BdrvRequestFlags flags)
{
BlockDriver *drv = bs->drv;
QEMUIOVector qiov;
struct iovec iov;
int ret;
struct iovec iov = {0};
int ret = 0;
/* TODO Emulate only part of misaligned requests instead of letting block
* drivers return -ENOTSUP and emulate everything */
int max_write_zeroes = bs->bl.max_write_zeroes ?
bs->bl.max_write_zeroes : MAX_WRITE_ZEROES_DEFAULT;
/* First try the efficient write zeroes operation */
if (drv->bdrv_co_write_zeroes) {
ret = drv->bdrv_co_write_zeroes(bs, sector_num, nb_sectors, flags);
if (ret != -ENOTSUP) {
return ret;
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) {
num = bs->bl.write_zeroes_alignment;
}
num -= sector_num % bs->bl.write_zeroes_alignment;
}
/* limit request size */
if (num > max_write_zeroes) {
num = max_write_zeroes;
}
ret = -ENOTSUP;
/* First try the efficient write zeroes operation */
if (drv->bdrv_co_write_zeroes) {
ret = drv->bdrv_co_write_zeroes(bs, sector_num, num, flags);
}
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);
}
qemu_iovec_init_external(&qiov, &iov, 1);
ret = drv->bdrv_co_writev(bs, sector_num, num, &qiov);
}
sector_num += num;
nb_sectors -= num;
}
/* Fall back to bounce buffer if write zeroes is unsupported */
iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE;
iov.iov_base = qemu_blockalign(bs, iov.iov_len);
memset(iov.iov_base, 0, iov.iov_len);
qemu_iovec_init_external(&qiov, &iov, 1);
ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, &qiov);
qemu_vfree(iov.iov_base);
return ret;
}