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