Reviewed-by: Josh Durgin <josh.durgin@xxxxxxxxxxx>
On 01/28/2013 02:09 PM, Alex Elder wrote:
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@xxxxxxxxxxx>
---
drivers/block/rbd.c | 37 ++++++++++++++++++++++++++++---------
1 file changed, 28 insertions(+), 9 deletions(-)
diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 177ba0c..107df40 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -262,7 +262,7 @@ struct rbd_device {
spinlock_t lock; /* queue lock */
struct rbd_image_header header;
- atomic_t exists;
+ unsigned long flags;
struct rbd_spec *spec;
char *header_name;
@@ -291,6 +291,12 @@ struct rbd_device {
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 */
@@ -790,7 +796,8 @@ static int rbd_dev_set_mapping(struct rbd_device
*rbd_dev)
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;
}
@@ -1886,9 +1893,14 @@ static void rbd_request_fn(struct request_queue *q)
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;
@@ -2578,7 +2590,7 @@ struct rbd_device *rbd_dev_create(struct
rbd_client *rbdc,
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);
@@ -3207,10 +3219,17 @@ static int rbd_dev_snaps_update(struct
rbd_device *rbd_dev)
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 ?
--
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