Re: [Qemu-devel] [PATCH 09/11] raw-posix: implement write_zeroes with MAY_UNMAP for block devices

[Peter Lieven]

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 <address@hidden>:

> 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 <address@hidden>
> ---
> 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
> 
>