diff options
Diffstat (limited to 'block/io.c')
| -rw-r--r-- | block/io.c | 20 |
1 files changed, 10 insertions, 10 deletions
diff --git a/block/io.c b/block/io.c index 305e0d952e..d4bc83b33b 100644 --- a/block/io.c +++ b/block/io.c @@ -236,12 +236,12 @@ static bool bdrv_requests_pending(BlockDriverState *bs) /* * Wait for pending requests to complete on a single BlockDriverState subtree * - * See the warning in bdrv_drain_all(). This function can only be called if - * you are sure nothing can generate I/O because you have op blockers - * installed. - * * Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState * AioContext. + * + * Only this BlockDriverState's AioContext is run, so in-flight requests must + * not depend on events in other AioContexts. In that case, use + * bdrv_drain_all() instead. */ void bdrv_drain(BlockDriverState *bs) { @@ -260,12 +260,6 @@ void bdrv_drain(BlockDriverState *bs) * * This function does not flush data to disk, use bdrv_flush_all() for that * after calling this function. - * - * Note that completion of an asynchronous I/O operation can trigger any - * number of other I/O operations on other devices---for example a coroutine - * can be arbitrarily complex and a constant flow of I/O can come until the - * coroutine is complete. Because of this, it is not possible to have a - * function to drain a single device's I/O queue. */ void bdrv_drain_all(void) { @@ -288,6 +282,12 @@ void bdrv_drain_all(void) } } + /* Note that completion of an asynchronous I/O operation can trigger any + * number of other I/O operations on other devices---for example a + * coroutine can submit an I/O request to another device in response to + * request completion. Therefore we must keep looping until there was no + * more activity rather than simply draining each device independently. + */ while (busy) { busy = false; |