bdrv_requests_pending is checking children to also wait until internal
requests (such as metadata writes) have completed. However, checking
children is in general overkill. Children requests can be of two kinds:
- requests caused by an operation on bs, e.g. a bdrv_aio_write to bs
causing a write to bs->file->bs. In this case, the parent's in_flight
count will always be incremented by at least one for every request in
the child.
- asynchronous metadata writes or flushes. Such writes can be started
even if bs's in_flight count is zero, but not after the .bdrv_drain
callback has been invoked.
This patch therefore changes bdrv_drain to finish I/O in the parent
(after which the parent's in_flight will be locked to zero), call
bdrv_drain (after which the parent will not generate I/O on the child
anymore), and then wait for internal I/O in the children to complete.
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
block/io.c | 54 ++++++++++++++++++++++++++++++++++++------------------
1 file changed, 36 insertions(+), 18 deletions(-)
diff --git a/block/io.c b/block/io.c
index 5e1fbf1..c634fbc 100644
--- a/block/io.c
+++ b/block/io.c
@@ -156,16 +156,33 @@ bool bdrv_requests_pending(BlockDriverState *bs)
return false;
}
-static void bdrv_drain_recurse(BlockDriverState *bs)
+static bool bdrv_drain_poll(BlockDriverState *bs)
+{
+ bool waited = false;
+
+ while (atomic_read(&bs->in_flight) > 0) {
+ aio_poll(bdrv_get_aio_context(bs), true);
+ waited = true;
+ }
+ return waited;
+}
+
+static bool bdrv_drain_io_recurse(BlockDriverState *bs)
{
BdrvChild *child;
+ bool waited;
+
+ waited = bdrv_drain_poll(bs);
if (bs->drv && bs->drv->bdrv_drain) {
bs->drv->bdrv_drain(bs);
}
+
QLIST_FOREACH(child, &bs->children, next) {
- bdrv_drain_recurse(child->bs);
+ waited |= bdrv_drain_io_recurse(child->bs);
}
+
+ return waited;
}
typedef struct {
@@ -174,14 +191,6 @@ typedef struct {
bool done;
} BdrvCoDrainData;
-static void bdrv_drain_poll(BlockDriverState *bs)
-{
- while (bdrv_requests_pending(bs)) {
- /* Keep iterating */
- aio_poll(bdrv_get_aio_context(bs), true);
- }
-}
-
static void bdrv_co_drain_bh_cb(void *opaque)
{
BdrvCoDrainData *data = opaque;
@@ -218,6 +227,20 @@ static void coroutine_fn
bdrv_co_yield_to_drain(BlockDriverState *bs)
assert(data.done);
}
+static void bdrv_co_drain_io_recurse(BlockDriverState *bs)
+{
+ BdrvChild *child;
+
+ bdrv_co_yield_to_drain(bs);
+ if (bs->drv && bs->drv->bdrv_drain) {
+ bs->drv->bdrv_drain(bs);
+ }
+
+ QLIST_FOREACH(child, &bs->children, next) {
+ bdrv_co_drain_io_recurse(child->bs);
+ }
+}
+
void bdrv_drained_begin(BlockDriverState *bs)
{
if (!bs->quiesce_counter++) {
@@ -226,11 +249,10 @@ void bdrv_drained_begin(BlockDriverState *bs)
}
bdrv_io_unplugged_begin(bs);
- bdrv_drain_recurse(bs);
if (qemu_in_coroutine()) {
- bdrv_co_yield_to_drain(bs);
+ bdrv_co_drain_io_recurse(bs);
} else {
- bdrv_drain_poll(bs);
+ bdrv_drain_io_recurse(bs);
}
bdrv_io_unplugged_end(bs);
}
@@ -299,7 +321,6 @@ void bdrv_drain_all(void)
aio_context_acquire(aio_context);
bdrv_parent_drained_begin(bs);
bdrv_io_unplugged_begin(bs);
- bdrv_drain_recurse(bs);
aio_context_release(aio_context);
if (!g_slist_find(aio_ctxs, aio_context)) {
@@ -322,10 +343,7 @@ void bdrv_drain_all(void)
aio_context_acquire(aio_context);
for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
if (aio_context == bdrv_get_aio_context(bs)) {
- if (bdrv_requests_pending(bs)) {
- aio_poll(aio_context, true);
- waited = true;
- }
+ waited |= bdrv_drain_io_recurse(bs);
}
}
aio_context_release(aio_context);
--
2.7.4
