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

[Zhi Yong Wu]

On Fri, Nov 11, 2011 at 5:10 PM, Kevin Wolf <address@hidden> wrote:
> Am 11.11.2011 05:06, schrieb 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?
>
> Just use the image file. Start a new qemu instance or whatever and
> you'll get the right data.
thanks.

>
> Kevin
>



-- 
Regards,

Zhi Yong Wu