Re: [Qemu-devel] [Qemu-block] [PATCH for-2.6 2/2] block: Fix blk_aio_write_zeroes()

[Max Reitz]

On 13.04.2016 13:06, Kevin Wolf wrote:
> Commit 57d6a428 broke blk_aio_write_zeroes() because in some write
> functions in the call path don't have an explicit length argument but
> reuse qiov->size instead. Which is great, except that write_zeroes
> doesn't have a qiov, which this commit interprets as 0 bytes.
> Consequently, blk_aio_write_zeroes() didn't effectively do anything.

You mean it has written null data? :-)

Alternative version: So it has written zero bytes? Works as intended, then.

> 
> This patch introduces an explicit acb->bytes in BlkAioEmAIOCB and uses
> that instead of acb->rwco.size.
> 
> The synchronous version of the function is okay because it does pass a
> qiov (with the right size and a NULL pointer as its base).
> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  block/block-backend.c      | 20 +++++++----
>  tests/qemu-iotests/033     |  8 +++--
>  tests/qemu-iotests/033.out | 82 
> ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 100 insertions(+), 10 deletions(-)
> 
> diff --git a/block/block-backend.c b/block/block-backend.c
> index d74f670..140c3f7 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c

[...]

> @@ -937,7 +940,8 @@ BlockAIOCB *blk_aio_write_zeroes(BlockBackend *blk, 
> int64_t sector_num,
>          return blk_abort_aio_request(blk, cb, opaque, -EINVAL);
>      }
>  
> -    return blk_aio_prwv(blk, sector_num << BDRV_SECTOR_BITS, NULL,
> +    return blk_aio_prwv(blk, sector_num << BDRV_SECTOR_BITS,
> +                        nb_sectors << BDRV_SECTOR_BITS, NULL,
>                          blk_aio_write_entry, BDRV_REQ_ZERO_WRITE, cb, 
> opaque);
>  }

Another thing about blk_aio_write_zeroes() that might need fixing is
that it completely ignores its flags parameter.

That can be done in a seperate patch, however (and is probably not
critical, as this currently just means that a potential REQ_MAY_UNMAP
from scsi-disk is ignored), so:

Reviewed-by: Max Reitz <address@hidden>

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