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

[Kevin Wolf <kwolf@redhat.com>]

Am 11.11.2011 05:06, schrieb Zhi Yong Wu:
> On Fri, Nov 11, 2011 at 1:32 AM, Kevin Wolf <kwolf@redhat.com> 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 <kwolf@redhat.com>
>> ---
>>  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.

Kevin