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 <f...@redhat.com> --- block/io.c | 17 +++++++++++++++++ include/block/block.h | 19 +++++++++++++++++++ include/block/block_int.h | 2 ++ 3 files changed, 38 insertions(+) diff --git a/block/io.c b/block/io.c index 5311473..630c1aa 100644 --- a/block/io.c +++ b/block/io.c @@ -2618,3 +2618,20 @@ 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)); +} diff --git a/include/block/block.h b/include/block/block.h index 6d70eb4..72ea9f4 100644 --- a/include/block/block.h +++ b/include/block/block.h @@ -624,4 +624,23 @@ void bdrv_flush_io_queue(BlockDriverState *bs); BlockAcctStats *bdrv_get_stats(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 diff --git a/include/block/block_int.h b/include/block/block_int.h index c0e6513..45dcabe 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -456,6 +456,8 @@ struct BlockDriverState { /* threshold limit for writes, in bytes. "High water mark". */ uint64_t write_threshold_offset; NotifierWithReturn write_threshold_notifier; + + int quiesce_counter; }; static inline BlockDriverState *backing_bs(BlockDriverState *bs) -- 2.4.3