block: .bdrv_open is non-coroutine and unlocked

Drivers were a bit confused about whether .bdrv_open can run in a
coroutine and whether or not it holds a graph lock.

It cannot keep a graph lock from the caller across the whole function
because it both changes the graph (requires a writer lock) and does I/O
(requires a reader lock). Therefore, it should take these locks
internally as needed.

The functions used to be called in coroutine context during image
creation. This was buggy for other reasons, and as of commit 32192301,
all block drivers go through no_co_wrappers. So it is not called in
coroutine context any more.

Fix qcow2 and qed to work with the correct assumptions: The graph lock
needs to be taken internally instead of just assuming it's already
there, and the coroutine path is dead code that can be removed.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20230504115750.54437-9-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 8 insertions, 10 deletions

diff --git a/block/qed.c b/block/qed.c
index aff2a20..be9ff0f 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -557,11 +557,13 @@ typedef struct QEDOpenCo {
     int ret;
 } QEDOpenCo;
 
-static void coroutine_fn GRAPH_RDLOCK bdrv_qed_open_entry(void *opaque)
+static void coroutine_fn bdrv_qed_open_entry(void *opaque)
 {
     QEDOpenCo *qoc = opaque;
     BDRVQEDState *s = qoc->bs->opaque;
 
+    GRAPH_RDLOCK_GUARD();
+
     qemu_co_mutex_lock(&s->table_lock);
     qoc->ret = bdrv_qed_do_open(qoc->bs, qoc->options, qoc->flags, qoc->errp);
     qemu_co_mutex_unlock(&s->table_lock);
@@ -579,21 +581,17 @@ static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,
     };
     int ret;
 
-    assume_graph_lock(); /* FIXME */
-
     ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
     if (ret < 0) {
         return ret;
     }
 
     bdrv_qed_init_state(bs);
-    if (qemu_in_coroutine()) {
-        bdrv_qed_open_entry(&qoc);
-    } else {
-        assert(qemu_get_current_aio_context() == qemu_get_aio_context());
-        qemu_coroutine_enter(qemu_coroutine_create(bdrv_qed_open_entry, &qoc));
-        BDRV_POLL_WHILE(bs, qoc.ret == -EINPROGRESS);
-    }
+    assert(!qemu_in_coroutine());
+    assert(qemu_get_current_aio_context() == qemu_get_aio_context());
+    qemu_coroutine_enter(qemu_coroutine_create(bdrv_qed_open_entry, &qoc));
+    BDRV_POLL_WHILE(bs, qoc.ret == -EINPROGRESS);
+
     return qoc.ret;
 }