block: Add bdrv_co_enter()/leave()

Add a pair of functions to temporarily move the current coroutine to the
AioContext of a given BlockDriverState.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20201005155855.256490-13-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/block.c b/block.c
index 52b2e2709f..8d9b9017d3 100644
--- a/block.c
+++ b/block.c
@@ -6303,6 +6303,29 @@ AioContext *bdrv_get_aio_context(BlockDriverState *bs)
     return bs ? bs->aio_context : qemu_get_aio_context();
 }
 
+AioContext *coroutine_fn bdrv_co_enter(BlockDriverState *bs)
+{
+    Coroutine *self = qemu_coroutine_self();
+    AioContext *old_ctx = qemu_coroutine_get_aio_context(self);
+    AioContext *new_ctx;
+
+    /*
+     * Increase bs->in_flight to ensure that this operation is completed before
+     * moving the node to a different AioContext. Read new_ctx only afterwards.
+     */
+    bdrv_inc_in_flight(bs);
+
+    new_ctx = bdrv_get_aio_context(bs);
+    aio_co_reschedule_self(new_ctx);
+    return old_ctx;
+}
+
+void coroutine_fn bdrv_co_leave(BlockDriverState *bs, AioContext *old_ctx)
+{
+    aio_co_reschedule_self(old_ctx);
+    bdrv_dec_in_flight(bs);
+}
+
 void bdrv_coroutine_enter(BlockDriverState *bs, Coroutine *co)
 {
     aio_co_enter(bdrv_get_aio_context(bs), co);