[PATCH 4/4] rbd: use snaps list in rbd_snap_by_name()

[Alex Elder <elder@inktank.com>]

An rbd_dev structure maintains a list of current snapshots that have
already been fully initialized.  The entries on the list have type
struct rbd_snap, and each entry contains a copy of information
that's found in the rbd_dev's snapshot context and header.

The only caller of snap_by_name() is rbd_header_set_snap().  In that
call site any positive return value (the index in the snapshot
array) is ignored.

rbd_header_set_snap() also has only one caller--rbd_add()--and that
call is made after a call to rbd_dev_snap_devs_update().  Because
the rbd_snap structures are initialized in that function, the
current snapshot list can be used instead of the snapshot context to
look up a snapshot's information by name.

Change snap_by_name() so it uses the snapshot list rather than the
rbd_dev's snapshot context in looking up snapshot information.
Return 0 if it's found rather than the snapshot id.  To do this,
change rbd_snap_by_name() to take an rbd_dev rather than
rbd_image_header structure pointer as its first argument.

No caller ever passes a null pointer to snap_by_name() for the
snapshot id or the size, so just assign using those pointers
unconditionally.

Signed-off-by: Alex Elder <elder@inktank.com>
---
 drivers/block/rbd.c |   19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index e922989..4dff92f 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -623,23 +623,18 @@ out_err:

 static int snap_by_name(struct rbd_device *rbd_dev, const char *snap_name)
 {
-	int i;
-	struct rbd_image_header *header = &rbd_dev->header;
-	char *p = header->snap_names;
-
-	rbd_assert(header->snapc != NULL);
-	for (i = 0; i < header->snapc->num_snaps; i++) {
-		if (!strcmp(snap_name, p)) {

-			/* Found it.  Pass back its id and/or size */
+	struct rbd_snap *snap;

-			rbd_dev->mapping.snap_id = header->snapc->snaps[i];
-			rbd_dev->mapping.size = header->snap_sizes[i];
+	list_for_each_entry(snap, &rbd_dev->snaps, node) {
+		if (!strcmp(snap_name, snap->name)) {
+			rbd_dev->mapping.snap_id = snap->id;
+			rbd_dev->mapping.size = snap->size;

-			return i;
+			return 0;
 		}
-		p += strlen(p) + 1;	/* Skip ahead to the next name */
 	}
+
 	return -ENOENT;
 }

-- 
1.7.9.5