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block: Introduce "drained begin/end" API

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The semantics is that after bdrv_drained_begin(bs), bs will not get new external
requests until the matching bdrv_drained_end(bs).

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fam Zheng 2015-10-23 11:08:09 +08:00 committed by Kevin Wolf
parent c1e1e5fa8f
commit 51288d7917
3 changed files with 38 additions and 0 deletions
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17
block/io.c
View file

@ -2624,3 +2624,20 @@ void bdrv_flush_io_queue(BlockDriverState *bs)
}
bdrv_start_throttled_reqs(bs);
}
void bdrv_drained_begin(BlockDriverState *bs)
{
if (!bs->quiesce_counter++) {
aio_disable_external(bdrv_get_aio_context(bs));
}
bdrv_drain(bs);
}
void bdrv_drained_end(BlockDriverState *bs)
{
assert(bs->quiesce_counter > 0);
if (--bs->quiesce_counter > 0) {
return;
}
aio_enable_external(bdrv_get_aio_context(bs));
}

19
include/block/block.h
View file

@ -610,4 +610,23 @@ void bdrv_io_plug(BlockDriverState *bs);
void bdrv_io_unplug(BlockDriverState *bs);
void bdrv_flush_io_queue(BlockDriverState *bs);
/**
* bdrv_drained_begin:
*
* Begin a quiesced section for exclusive access to the BDS, by disabling
* external request sources including NBD server and device model. Note that
* this doesn't block timers or coroutines from submitting more requests, which
* means block_job_pause is still necessary.
*
* This function can be recursive.
*/
void bdrv_drained_begin(BlockDriverState *bs);
/**
* bdrv_drained_end:
*
* End a quiescent section started by bdrv_drained_begin().
*/
void bdrv_drained_end(BlockDriverState *bs);
#endif

2
include/block/block_int.h
View file

@ -448,6 +448,8 @@ struct BlockDriverState {
/* threshold limit for writes, in bytes. "High water mark". */
uint64_t write_threshold_offset;
NotifierWithReturn write_threshold_notifier;
int quiesce_counter;
};
struct BlockBackendRootState {