@@ -286,12 +286,21 @@ static bool bdrv_drain_one(BlockDriverState *bs)
*
* Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState
* AioContext.
+ *
+ * Devices are paused to avoid looping forever because otherwise they could
+ * keep submitting more requests.
*/
void bdrv_drain(BlockDriverState *bs)
{
+ Error *blocker = NULL;
+
+ error_setg(&blocker, "bdrv_drain in progress");
+ bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
while (bdrv_drain_one(bs)) {
/* Keep iterating */
}
+ bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
+ error_free(blocker);
}
/*
@@ -303,14 +312,20 @@ void bdrv_drain(BlockDriverState *bs)
* 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.
+ * coroutine is complete. Because of this, we must call bdrv_drain_one in a
+ * loop.
+ *
+ * We explicitly pause block jobs and devices to prevent them from submitting
+ * more requests.
*/
void bdrv_drain_all(void)
{
/* Always run first iteration so any pending completion BHs run */
bool busy = true;
BlockDriverState *bs = NULL;
+ Error *blocker = NULL;
+
+ error_setg(&blocker, "bdrv_drain_all in progress");
while ((bs = bdrv_next(bs))) {
AioContext *aio_context = bdrv_get_aio_context(bs);
@@ -319,6 +334,7 @@ void bdrv_drain_all(void)
if (bs->job) {
block_job_pause(bs->job);
}
+ bdrv_op_block(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
aio_context_release(aio_context);
}
@@ -343,8 +359,10 @@ void bdrv_drain_all(void)
if (bs->job) {
block_job_resume(bs->job);
}
+ bdrv_op_unblock(bs, BLOCK_OP_TYPE_DEVICE_IO, blocker);
aio_context_release(aio_context);
}
+ error_free(blocker);
}
/**
We don't want new requests from guest, so block the operation around the nested poll. It also avoids looping forever when iothread is submitting a lot of requests. Signed-off-by: Fam Zheng <famz@redhat.com> --- block/io.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-)