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>
---
v1->v2: moved bdrv_drain callback after in_flight is 0
in the parent [from QED drain discussion]
block/io.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)
diff --git a/block/io.c b/block/io.c
index a9a23a6..db975ab 100644
--- a/block/io.c
+++ b/block/io.c
@@ -237,16 +237,25 @@ bool bdrv_requests_pending(BlockDriverState *bs)
return false;
}
-static void bdrv_drain_recurse(BlockDriverState *bs)
+static bool bdrv_drain_io_recurse(BlockDriverState *bs)
{
BdrvChild *child;
+ bool waited = false;
+
+ while (atomic_read(&bs->in_flight) > 0) {
+ aio_poll(bdrv_get_aio_context(bs), true);
+ waited = true;
+ }
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;
}
/*
@@ -264,11 +273,7 @@ void bdrv_drain(BlockDriverState *bs)
{
bdrv_no_throttling_begin(bs);
bdrv_io_unplugged_begin(bs);
- bdrv_drain_recurse(bs);
- while (bdrv_requests_pending(bs)) {
- /* Keep iterating */
- aio_poll(bdrv_get_aio_context(bs), true);
- }
+ bdrv_drain_io_recurse(bs);
bdrv_io_unplugged_end(bs);
bdrv_no_throttling_end(bs);
}
@@ -295,7 +300,6 @@ void bdrv_drain_all(void)
}
bdrv_no_throttling_begin(bs);
bdrv_io_unplugged_begin(bs);
- bdrv_drain_recurse(bs);
aio_context_release(aio_context);
if (!g_slist_find(aio_ctxs, aio_context)) {
@@ -319,10 +323,7 @@ void bdrv_drain_all(void)
aio_context_acquire(aio_context);
while ((bs = bdrv_next(bs))) {
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);
--
1.8.3.1
