Wouldn't it be good to add bdi->can_write_zeroes_with_unmap here as well?
This would automatically avoid full allocation when converting something to a
host device
supporting BLKDISCARDZEROES.
Peter
Am 12.11.2013 um 16:49 schrieb Paolo Bonzini <pbonz...@redhat.com>:
> See the next commit for the description of the Linux kernel problem
> that is worked around in raw_open_common.
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> block/raw-posix.c | 38 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index 830e109..5cb46f1 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -335,6 +335,23 @@ static int raw_open_common(BlockDriverState *bs, QDict
> *options,
> if (S_ISREG(st.st_mode)) {
> s->discard_zeroes = true;
> }
> +#ifdef BLKDISCARDZEROES
> + if (S_ISBLK(st.st_mode)) {
> + unsigned int arg;
> + if (ioctl(s->fd, BLKDISCARDZEROES, &arg) == 0 && arg) {
> + s->discard_zeroes = true;
> + }
> + }
> +#endif
> +#ifdef CONFIG_LINUX
> + /* On Linux 3.10, BLKDISCARD leaves stale data in the page cache. Do
> + * not rely on the contents of discarded blocks unless using O_DIRECT.
> + */
> + if (!(bs->open_flags & BDRV_O_NOCACHE)) {
> + s->discard_zeroes = false;
> + }
> +#endif
> + }
>
> #ifdef CONFIG_XFS
> if (platform_test_xfs_fd(s->fd)) {
> @@ -1587,6 +1604,26 @@ static coroutine_fn BlockDriverAIOCB
> *hdev_aio_discard(BlockDriverState *bs,
> cb, opaque, QEMU_AIO_DISCARD|QEMU_AIO_BLKDEV);
> }
>
> +static coroutine_fn int hdev_co_write_zeroes(BlockDriverState *bs,
> + int64_t sector_num, int nb_sectors, BdrvRequestFlags flags)
> +{
> + BDRVRawState *s = bs->opaque;
> + int rc;
> +
> + rc = fd_open(bs);
> + if (rc < 0) {
> + return rc;
> + }
> + if (!(flags & BDRV_REQ_MAY_UNMAP)) {
> + return -ENOTSUP;
> + }
> + if (!s->discard_zeroes) {
> + return -ENOTSUP;
> + }
> + return paio_submit_co(bs, s->fd, sector_num, NULL, nb_sectors,
> + QEMU_AIO_DISCARD|QEMU_AIO_BLKDEV);
> +}
> +
> static int hdev_create(const char *filename, QEMUOptionParameter *options,
> Error **errp)
> {
> @@ -1639,6 +1676,7 @@ static BlockDriver bdrv_host_device = {
> .bdrv_reopen_abort = raw_reopen_abort,
> .bdrv_create = hdev_create,
> .create_options = raw_create_options,
> + .bdrv_co_write_zeroes = hdev_co_write_zeroes,
>
> .bdrv_aio_readv = raw_aio_readv,
> .bdrv_aio_writev = raw_aio_writev,
> --
> 1.8.4.2
>
>
