[Qemu-devel] Re: [PATCH 1/4] block: clarify the meaning of BDRV_O_NOCACHE

[Kevin Wolf <kwolf@redhat.com>]

Am 16.03.2011 10:42, schrieb Stefan Hajnoczi:
> On Tue, Mar 15, 2011 at 2:11 PM, Christoph Hellwig <hch@lst.de> wrote:
>> Change BDRV_O_NOCACHE to only imply bypassing the host OS file cache,
>> but no writeback semantics.  All existing callers are changed to also
>> specify BDRV_O_CACHE_WB to give them writeback semantics.
>>
>> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> I think there is one hunk missing:
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 75b8bec..db1931b 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -229,7 +229,7 @@ static int qcow2_open(BlockDriverState *bs, int flags)
>      }
> 
>      /* alloc L2 table/refcount block cache */
> -    writethrough = ((flags & BDRV_O_CACHE_MASK) == 0);
> +    writethrough = ((flags & (BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH)) == 0);
>      s->l2_table_cache = qcow2_cache_create(bs, L2_CACHE_SIZE, writethrough);
>      s->refcount_block_cache = qcow2_cache_create(bs, REFCOUNT_CACHE_SIZE,
>          writethrough);

This one doesn't make a difference. But the intention could be made
clearer now that all writeback modes have BDRV_O_CACHE_WB set:

    writethrough = ((flags & BDRV_O_CACHE_WB) == 0);

Kevin