Re: [Qemu-devel] [PATCH v2 17/17] block: Move request_alignment into BlockLimit

[Kevin Wolf]

Am 14.06.2016 um 23:30 hat Eric Blake geschrieben:
> It makes more sense to have ALL block size limit constraints
> in the same struct.  Improve the documentation while at it.
> 
> Signed-off-by: Eric Blake <address@hidden>
> 
> ---
> v2: drop hacks for save/restore of alignment, now that earlier
> patches handled setting up BlockLimits more sanely
> ---
>  include/block/block_int.h | 22 +++++++++++++---------
>  block.c                   |  2 +-
>  block/blkdebug.c          |  4 ++--
>  block/bochs.c             |  2 +-
>  block/cloop.c             |  2 +-
>  block/dmg.c               |  2 +-
>  block/io.c                | 12 ++++++------
>  block/iscsi.c             |  2 +-
>  block/qcow2.c             |  2 +-
>  block/raw-posix.c         | 16 ++++++++--------
>  block/raw-win32.c         |  6 +++---
>  block/vvfat.c             |  2 +-
>  12 files changed, 39 insertions(+), 35 deletions(-)
> 
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 88ef826..77f47d9 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -324,6 +324,12 @@ struct BlockDriver {
>  };
> 
>  struct BlockLimits {
> +    /* Alignment requirement, in bytes, for offset/length of I/O
> +     * requests. Must be a power of 2 less than INT_MAX. A value of 0
> +     * defaults to 1 for drivers with modern byte interfaces, and to
> +     * 512 otherwise. */

No, a value of zero probably crashes qemu. The defaults apply when they
aren't overridden by the driver, but this field is always non-zero.

> +    uint32_t request_alignment;
> +
>      /* maximum number of bytes that can be discarded at once (since it
>       * is signed, it must be < 2G, if set), should be multiple of
>       * pdiscard_alignment, but need not be power of 2. May be 0 if no

Kevin