[1/2] Add no-op aio emulation stub

We need to be able to do nothing in AIO fashion. Since I suspect this
could be useful for more cases than the non flushing, I figured I'd
create a new function that does everything AIO-like, but doesn't do
anything.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 block.c |   18 ++++++++++++++++++
 block.h |    5 +++++
 2 files changed, 23 insertions(+), 0 deletions(-)

bdrv_aio_noop_em() could be useful for benchmarking and optimizing the
aio code.  It serves as a cheap operation that lets us see the cost of
the aio roundtrip.

Stefan

Am 10.05.2010 23:51, schrieb Alexander Graf:
> We need to be able to do nothing in AIO fashion. Since I suspect this
> could be useful for more cases than the non flushing, I figured I'd
> create a new function that does everything AIO-like, but doesn't do
> anything.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  block.c |   18 ++++++++++++++++++
>  block.h |    5 +++++
>  2 files changed, 23 insertions(+), 0 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 48305b7..1cd39d7 100644
> --- a/block.c
> +++ b/block.c
> @@ -2196,6 +2196,24 @@ static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,
>      return &acb->common;
>  }
>  
> +BlockDriverAIOCB *bdrv_aio_noop_em(BlockDriverState *bs,
> +        BlockDriverCompletionFunc *cb, void *opaque)
> +{
> +    BlockDriverAIOCBSync *acb;
> +
> +    acb = qemu_aio_get(&bdrv_em_aio_pool, bs, cb, opaque);
> +    acb->is_write = 1; /* don't bounce in the completion hadler */

Typo in the comment.

> +    acb->qiov = NULL;
> +    acb->bounce = NULL;
> +    acb->ret = 0;
> +
> +    if (!acb->bh)
> +        acb->bh = qemu_bh_new(bdrv_aio_bh_cb, acb);
> +
> +    qemu_bh_schedule(acb->bh);
> +    return &acb->common;
> +}
> +
>  /**************************************************************/
>  /* sync block device emulation */
>  
> diff --git a/block.h b/block.h
> index f87d24e..bef6358 100644
> --- a/block.h
> +++ b/block.h
> @@ -33,6 +33,7 @@ typedef struct QEMUSnapshotInfo {
>  #define BDRV_O_CACHE_WB    0x0040 /* use write-back caching */
>  #define BDRV_O_NATIVE_AIO  0x0080 /* use native AIO instead of the thread pool */
>  #define BDRV_O_NO_BACKING  0x0100 /* don't open the backing file */
> +#define BDRV_O_NOFLUSH     0x0200 /* don't flush the image ever */
>  
>  #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_CACHE_WB)

This hunk should be in patch 2/2.

>  
> @@ -97,6 +98,10 @@ BlockDriverAIOCB *bdrv_aio_flush(BlockDriverState *bs,
>  				 BlockDriverCompletionFunc *cb, void *opaque);
>  void bdrv_aio_cancel(BlockDriverAIOCB *acb);
>  
> +/* Emulate a no-op */
> +BlockDriverAIOCB *bdrv_aio_noop_em(BlockDriverState *bs,
> +        BlockDriverCompletionFunc *cb, void *opaque);
> +
>  typedef struct BlockRequest {
>      /* Fields to be filled by multiwrite caller */
>      int64_t sector;

I think exporting this function shouldn't be necessary. Everything that
deals with AIO emulation should be contained in block.c.

Kevin