Re: [Qemu-devel] [PULL 4/9] block: workaround for unaligned byte range in fallocate()

[Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>]

Many thanks

Andrey

On 05/09/2019 21:21, Eric Blake wrote:
> From: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> 
> Revert the commit 118f99442d 'block/io.c: fix for the allocation failure'
> and use better error handling for file systems that do not support
> fallocate() for an unaligned byte range. Allow falling back to pwrite
> in case fallocate() returns EINVAL.
> 
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Suggested-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Reviewed-by: Denis V. Lunev <den@openvz.org>
> Message-Id: <1566913973-15490-1-git-send-email-andrey.shinkevich@virtuozzo.com>
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>   block/io.c         | 2 +-
>   block/file-posix.c | 7 +++++++
>   2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/block/io.c b/block/io.c
> index 0fa10831edb7..16a598fd0857 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1746,7 +1746,7 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
>               assert(!bs->supported_zero_flags);
>           }
> 
> -        if (ret < 0 && !(flags & BDRV_REQ_NO_FALLBACK)) {
> +        if (ret == -ENOTSUP && !(flags & BDRV_REQ_NO_FALLBACK)) {
>               /* Fall back to bounce buffer if write zeroes is unsupported */
>               BdrvRequestFlags write_flags = flags & ~BDRV_REQ_ZERO_WRITE;
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 71f168ee2f13..87c5a4ccbdc8 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1588,6 +1588,13 @@ static int handle_aiocb_write_zeroes(void *opaque)
>       if (s->has_write_zeroes) {
>           int ret = do_fallocate(s->fd, FALLOC_FL_ZERO_RANGE,
>                                  aiocb->aio_offset, aiocb->aio_nbytes);
> +        if (ret == -EINVAL) {
> +            /*
> +             * Allow falling back to pwrite for file systems that
> +             * do not support fallocate() for an unaligned byte range.
> +             */
> +            return -ENOTSUP;
> +        }
>           if (ret == 0 || ret != -ENOTSUP) {
>               return ret;
>           }
> 

-- 
With the best regards,
Andrey Shinkevich