Re: [Qemu-devel] [PATCH] block: workaround for unaligned byte range in fallocate()

[Eric Blake <eblake@redhat.com>]

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On 8/22/19 1:31 PM, Andrey Shinkevich wrote:
> Revert the commit 118f99442d 'block/io.c: fix for the allocation failure'
> and make better error handling for the file systems that do not support

s/make/use/

> fallocate() for the unaligned byte range. Allow falling back to pwrite

s/the/an/

> 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>
> ---
> Discussed in email thread with the message ID
> <1554474244-553661-1-git-send-email-andrey.shinkevich@virtuozzo.com>
> 
>  block/file-posix.c | 7 +++++++
>  block/io.c         | 2 +-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index fbeb006..2c254ff 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 unaligned byte range.

s/for/for an/

> +             */
> +            return -ENOTSUP;
> +        }
>          if (ret == 0 || ret != -ENOTSUP) {
>              return ret;
>          }
> diff --git a/block/io.c b/block/io.c
> index 56bbf19..58f08cd 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1558,7 +1558,7 @@ 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;
>  
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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