rbd: define flags field, use it for exists flag
Define a new rbd device flags field, manipulated using bit
operations. Replace the use of the current "exists" flag with a bit
in this new "flags" field. Add a little commentary about the
"exists" flag, which does not need to be manipulated atomically.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index fd9656b..8c90a39 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -264,7 +264,7 @@
spinlock_t lock; /* queue lock */
struct rbd_image_header header;
- atomic_t exists;
+ unsigned long flags;
struct rbd_spec *spec;
char *header_name;
@@ -292,6 +292,12 @@
unsigned long open_count;
};
+/* Flag bits for rbd_dev->flags */
+
+enum rbd_dev_flags {
+ RBD_DEV_FLAG_EXISTS, /* mapped snapshot has not been deleted */
+};
+
static DEFINE_MUTEX(ctl_mutex); /* Serialize open/close/setup/teardown */
static LIST_HEAD(rbd_dev_list); /* devices */
@@ -782,7 +788,8 @@
goto done;
rbd_dev->mapping.read_only = true;
}
- atomic_set(&rbd_dev->exists, 1);
+ set_bit(RBD_DEV_FLAG_EXISTS, &rbd_dev->flags);
+
done:
return ret;
}
@@ -1877,9 +1884,14 @@
rbd_assert(rbd_dev->spec->snap_id == CEPH_NOSNAP);
}
- /* Quit early if the snapshot has disappeared */
-
- if (!atomic_read(&rbd_dev->exists)) {
+ /*
+ * Quit early if the mapped snapshot no longer
+ * exists. It's still possible the snapshot will
+ * have disappeared by the time our request arrives
+ * at the osd, but there's no sense in sending it if
+ * we already know.
+ */
+ if (!test_bit(RBD_DEV_FLAG_EXISTS, &rbd_dev->flags)) {
dout("request for non-existent snapshot");
rbd_assert(rbd_dev->spec->snap_id != CEPH_NOSNAP);
result = -ENXIO;
@@ -2571,7 +2583,7 @@
return NULL;
spin_lock_init(&rbd_dev->lock);
- atomic_set(&rbd_dev->exists, 0);
+ rbd_dev->flags = 0;
INIT_LIST_HEAD(&rbd_dev->node);
INIT_LIST_HEAD(&rbd_dev->snaps);
init_rwsem(&rbd_dev->header_rwsem);
@@ -3200,10 +3212,17 @@
if (snap_id == CEPH_NOSNAP || (snap && snap->id > snap_id)) {
struct list_head *next = links->next;
- /* Existing snapshot not in the new snap context */
-
+ /*
+ * A previously-existing snapshot is not in
+ * the new snap context.
+ *
+ * If the now missing snapshot is the one the
+ * image is mapped to, clear its exists flag
+ * so we can avoid sending any more requests
+ * to it.
+ */
if (rbd_dev->spec->snap_id == snap->id)
- atomic_set(&rbd_dev->exists, 0);
+ clear_bit(RBD_DEV_FLAG_EXISTS, &rbd_dev->flags);
rbd_remove_snap_dev(snap);
dout("%ssnap id %llu has been removed\n",
rbd_dev->spec->snap_id == snap->id ?
