Re: [Qemu-devel] [PATCH v3 09/22] blkdebug: Set request_alignment during .bdrv_refresh_limits()

[Fam Zheng <famz@redhat.com>]

On Thu, 06/23 16:37, Eric Blake wrote:
> We want to eventually stick request_alignment alongside other
> BlockLimits, but first, we must ensure it is populated at the
> same time as all other limits, rather than being a special case
> that is set only when a block is first opened.
> 
> Note that when the user does not provide "align", then we were
> defaulting to bs->request_alignment - but at this stage in the
> initialization, that was always 512.  We were also rejecting an
> explicit "align":0 from the user; this patch now allows that,
> as an explicit request for the default alignment (which may not
> always be 512 in the future).
> 
> qemu-iotests 77 is particularly sensitive to the fact that we
> can specify an artificial alignment override in blkdebug, and
> that override must continue to work even when limits are
> refreshed on an already open device.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v3: rework to allow user to specify "align":0 for default
> v2: new patch
> ---
>  qapi/block-core.json |  3 ++-
>  block/blkdebug.c     | 19 +++++++++++++++----
>  2 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 98a20d2..ac8f5f6 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1961,7 +1961,8 @@
>  #
>  # @config:          #optional filename of the configuration file
>  #
> -# @align:           #optional required alignment for requests in bytes
> +# @align:           #optional required alignment for requests in bytes,
> +#                   must be power of 2, or 0 for default
>  #
>  # @inject-error:    #optional array of error injection descriptions
>  #
> diff --git a/block/blkdebug.c b/block/blkdebug.c
> index 20d25bd..54b6870 100644
> --- a/block/blkdebug.c
> +++ b/block/blkdebug.c
> @@ -37,6 +37,7 @@
>  typedef struct BDRVBlkdebugState {
>      int state;
>      int new_state;
> +    int align;
> 
>      QLIST_HEAD(, BlkdebugRule) rules[BLKDBG__MAX];
>      QSIMPLEQ_HEAD(, BlkdebugRule) active_rules;
> @@ -382,10 +383,10 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
>      }
> 
>      /* Set request alignment */
> -    align = qemu_opt_get_size(opts, "align", bs->request_alignment);
> -    if (align > 0 && align < INT_MAX && !(align & (align - 1))) {
> -        bs->request_alignment = align;
> -    } else {
> +    align = qemu_opt_get_size(opts, "align", 0);
> +    if (align < INT_MAX && is_power_of_2(align)) {
> +        s->align = align;
> +    } else if (align) {
>          error_setg(errp, "Invalid alignment");
>          ret = -EINVAL;
>          goto fail_unref;
> @@ -720,6 +721,15 @@ static void blkdebug_refresh_filename(BlockDriverState *bs, QDict *options)
>      bs->full_open_options = opts;
>  }
> 
> +static void blkdebug_refresh_limits(BlockDriverState *bs, Error **errp)
> +{
> +    BDRVBlkdebugState *s = bs->opaque;
> +
> +    if (s->align) {
> +        bs->request_alignment = s->align;
> +    }
> +}
> +
>  static int blkdebug_reopen_prepare(BDRVReopenState *reopen_state,
>                                     BlockReopenQueue *queue, Error **errp)
>  {
> @@ -738,6 +748,7 @@ static BlockDriver bdrv_blkdebug = {
>      .bdrv_getlength         = blkdebug_getlength,
>      .bdrv_truncate          = blkdebug_truncate,
>      .bdrv_refresh_filename  = blkdebug_refresh_filename,
> +    .bdrv_refresh_limits    = blkdebug_refresh_limits,
> 
>      .bdrv_aio_readv         = blkdebug_aio_readv,
>      .bdrv_aio_writev        = blkdebug_aio_writev,
> -- 
> 2.5.5
> 

Reviewed-by: Fam Zheng <famz@redhat.com>