There are times when the QEMU main loop wishes to drain I/O requests.
Up until now bdrv_drain_all() meant that no new guest I/O will be
processed until the next event loop iteration.
This is no longer true with dataplane since it runs outside the QEMU
global mutex. The BlockDevOps->drain_threads_cb() interface allows the
device model to drain and stop threads. Once draining completes, the
QEMU main loop can be sure that no further I/O will take place until
next main loop iteration.
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
block.c | 6 ++++++
include/block/block.h | 9 +++++++++
2 files changed, 15 insertions(+)
diff --git a/block.c b/block.c
index 1c9df27..a3323b2 100644
--- a/block.c
+++ b/block.c
@@ -1430,6 +1430,12 @@ void bdrv_drain_all(void)
BlockDriverState *bs;
bool busy;
+ QTAILQ_FOREACH(bs, &bdrv_states, list) {
+ if (bs->dev_ops && bs->dev_ops->drain_threads_cb) {
+ bs->dev_ops->drain_threads_cb(bs->dev_opaque);
+ }
+ }
+
do {
busy = qemu_aio_wait();
diff --git a/include/block/block.h b/include/block/block.h
index 2307f67..85147bb 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -60,6 +60,15 @@ typedef struct BlockDevOps {
* Runs when the size changed (e.g. monitor command block_resize)
*/
void (*resize_cb)(void *opaque);
+ /*
+ * Notifies the device model to drain any emulation threads
+ *
+ * Upon return, there must be no new or pending requests outside the QEMU
+ * main loop. The device model may restart emulation threads after this
+ * main loop iteration, for example in a hardware register handler
+ * function.
+ */
+ void (*drain_threads_cb)(void *opaque);
} BlockDevOps;
#define BDRV_O_RDWR 0x0002
--
1.8.1.4
