rbd: use a single value of snap_name to mean no snap

There's already a constant for this anyway.

Since rbd_header_set_snap() is only used to set the rbd device
snap_name field, just do that within that function rather than
having it take the snap_name as an argument.

Signed-off-by: Alex Elder <elder@dreamhost.com>
Signed-off-by: Sage Weil <sage@newdream.net>
v2: Changed interface rbd_header_set_snap() so it explicitly updates
    the snap_name in the rbd_device.  Also added a BUILD_BUG_ON()
    to verify the size of the snap_name field is sufficient for
    SNAP_HEAD_NAME.

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index dcdfe8d..d8d052d 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -553,20 +553,18 @@ static int snap_by_name(struct rbd_image_header *header, const char *snap_name,
        return i;
 }
 
-static int rbd_header_set_snap(struct rbd_device *dev,
-                              const char *snap_name,
-                              u64 *size)
+static int rbd_header_set_snap(struct rbd_device *dev, u64 *size)
 {
        struct rbd_image_header *header = &dev->header;
        struct ceph_snap_context *snapc = header->snapc;
        int ret = -ENOENT;
 
+       BUILD_BUG_ON(sizeof (dev->snap_name) < sizeof (RBD_SNAP_HEAD_NAME));
+
        down_write(&header->snap_rwsem);
 
-       if (!snap_name ||
-           !*snap_name ||
-           strcmp(snap_name, "-") == 0 ||
-           strcmp(snap_name, RBD_SNAP_HEAD_NAME) == 0) {
+       if (!memcmp(dev->snap_name, RBD_SNAP_HEAD_NAME,
+                   sizeof (RBD_SNAP_HEAD_NAME))) {
                if (header->total_snaps)
                        snapc->seq = header->snap_seq;
                else
@@ -576,7 +574,7 @@ static int rbd_header_set_snap(struct rbd_device *dev,
                if (size)
                        *size = header->image_size;
        } else {
-               ret = snap_by_name(header, snap_name, &snapc->seq, size);
+               ret = snap_by_name(header, dev->snap_name, &snapc->seq, size);
                if (ret < 0)
                        goto done;
 
@@ -1729,7 +1727,7 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
        if (rc)
                return rc;
 
-       rc = rbd_header_set_snap(rbd_dev, rbd_dev->snap_name, &total_size);
+       rc = rbd_header_set_snap(rbd_dev, &total_size);
        if (rc)
                return rc;
 
@@ -2215,7 +2213,8 @@ static ssize_t rbd_add(struct bus_type *bus,
        }
 
        if (rbd_dev->snap_name[0] == 0)
-               rbd_dev->snap_name[0] = '-';
+               memcpy(rbd_dev->snap_name, RBD_SNAP_HEAD_NAME,
+                       sizeof (RBD_SNAP_HEAD_NAME));
 
        rbd_dev->obj_len = strlen(rbd_dev->obj);
        snprintf(rbd_dev->obj_md_name, sizeof(rbd_dev->obj_md_name), "%s%s",