Re: [Qemu-devel] [PATCH 5/5] block: Move request_alignment into BlockLimit

[Eric Blake <eblake@redhat.com>]

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On 06/03/2016 11:03 AM, Eric Blake wrote:
> It makes more sense to have ALL block size limit constraints
> in the same struct.  Improve the documentation while at it.
> 
> Note that bdrv_refresh_limits() has to keep things alive across
> a memset() of BlockLimits.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  include/block/block_int.h | 12 ++++++++----
>  block.c                   |  4 ++--
>  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/raw-posix.c         | 16 ++++++++--------
>  block/raw-win32.c         |  6 +++---
>  block/vvfat.c             |  2 +-
>  11 files changed, 35 insertions(+), 29 deletions(-)

Something in this patch is causing qemu-iotests 77 to infloop; we may
decide it is just easier to drop this patch rather than find all the
places where the request_alignment must be preserved across what
otherwise zeroes out limits.

> +++ b/block/io.c
> @@ -71,8 +71,10 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
>  {
>      BlockDriver *drv = bs->drv;
>      Error *local_err = NULL;
> +    uint32_t request_alignment = bs->bl.request_alignment;
> 
>      memset(&bs->bl, 0, sizeof(bs->bl));
> +    bs->bl.request_alignment = request_alignment;

Or put another way, it looks like I missed another case where moving the
scope of the variable can impact who is expecting the value to remain
unchanged across certain operations.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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