Re: [Qemu-devel] [PATCH v2 2/3] block: Introduce bdrv_co_flush_to_os

[Zhi Yong Wu]

On Fri, Nov 11, 2011 at 1:32 AM, Kevin Wolf <address@hidden> wrote:
> qcow2 has a writeback metadata cache, so flushing a qcow2 image actually
> consists of writing back that cache to the protocol and only then flushes the
> protocol in order to get everything stable on disk.
>
> This introduces a separate bdrv_co_flush_to_os to reflect the split.
>
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  block.c       |   13 ++++++++++++-
>  block/qcow2.c |   10 ++++++++--
>  block_int.h   |    7 +++++++
>  3 files changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/block.c b/block.c
> index d3042da..f81dd9f 100644
> --- a/block.c
> +++ b/block.c
> @@ -2782,11 +2782,22 @@ static void coroutine_fn bdrv_flush_co_entry(void 
> *opaque)
>
>  int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>  {
> +    int ret;
> +
>     if (bs->open_flags & BDRV_O_NO_FLUSH) {
>         return 0;
>     } else if (!bs->drv) {
>         return 0;
> -    } else if (bs->drv->bdrv_co_flush_to_disk) {
> +    }
> +
> +    if (bs->drv->bdrv_co_flush_to_os) {
> +        ret = bs->drv->bdrv_co_flush_to_os(bs);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +
> +    if (bs->drv->bdrv_co_flush_to_disk) {
>         return bs->drv->bdrv_co_flush_to_disk(bs);
>     } else if (bs->drv->bdrv_aio_flush) {
>         BlockDriverAIOCB *acb;
> diff --git a/block/qcow2.c b/block/qcow2.c
> index f7f73fe..5c784ee 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1105,7 +1105,7 @@ fail:
>     return ret;
>  }
>
> -static int qcow2_co_flush(BlockDriverState *bs)
> +static int qcow2_co_flush_to_os(BlockDriverState *bs)
>  {
>     BDRVQcowState *s = bs->opaque;
>     int ret;
> @@ -1124,6 +1124,11 @@ static int qcow2_co_flush(BlockDriverState *bs)
>     }
>     qemu_co_mutex_unlock(&s->lock);
>
> +    return 0;
> +}
> +
> +static int qcow2_co_flush_to_disk(BlockDriverState *bs)
> +{
>     return bdrv_co_flush(bs->file);
>  }
>
> @@ -1245,7 +1250,8 @@ static BlockDriver bdrv_qcow2 = {
>
>     .bdrv_co_readv          = qcow2_co_readv,
>     .bdrv_co_writev         = qcow2_co_writev,
> -    .bdrv_co_flush_to_disk  = qcow2_co_flush,
> +    .bdrv_co_flush_to_os    = qcow2_co_flush_to_os,
> +    .bdrv_co_flush_to_disk  = qcow2_co_flush_to_disk,
>
>     .bdrv_co_discard        = qcow2_co_discard,
>     .bdrv_truncate          = qcow2_truncate,
> diff --git a/block_int.h b/block_int.h
> index 5aadc1f..1ec4921 100644
> --- a/block_int.h
> +++ b/block_int.h
> @@ -93,6 +93,13 @@ struct BlockDriver {
>      */
>     int coroutine_fn (*bdrv_co_flush_to_disk)(BlockDriverState *bs);
>
> +    /*
> +     * Flushes all internal caches to the OS. The data may still sit in a
> +     * writeback cache of the host OS, but it will survive a crash of the 
> qemu
Sorry, How to use the data in cache of host OS to survive  acrash of the qemu?

> +     * process.
> +     */
> +    int coroutine_fn (*bdrv_co_flush_to_os)(BlockDriverState *bs);
> +
>     int (*bdrv_aio_multiwrite)(BlockDriverState *bs, BlockRequest *reqs,
>         int num_reqs);
>     int (*bdrv_merge_requests)(BlockDriverState *bs, BlockRequest* a,
> --
> 1.7.6.4
>
>
>



-- 
Regards,

Zhi Yong Wu