ceph: fix incorrectly showing the .snap size for stat

We should set the 'stat->size' to the real number of snapshots for
snapdirs.

Link: https://tracker.ceph.com/issues/57342
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/inode.c

@@ -2449,6 +2449,7 @@ int ceph_getattr(struct user_namespace *mnt_userns, const struct path *path,
 		 struct kstat *stat, u32 request_mask, unsigned int flags)
 {
 	struct inode *inode = d_inode(path->dentry);
+	struct super_block *sb = inode->i_sb;
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	u32 valid_mask = STATX_BASIC_STATS;
 	int err = 0;
@@ -2478,16 +2479,34 @@ int ceph_getattr(struct user_namespace *mnt_userns, const struct path *path,
 	}
 
 	if (ceph_snap(inode) == CEPH_NOSNAP)
-		stat->dev = inode->i_sb->s_dev;
+		stat->dev = sb->s_dev;
 	else
 		stat->dev = ci->i_snapid_map ? ci->i_snapid_map->dev : 0;
 
 	if (S_ISDIR(inode->i_mode)) {
-		if (ceph_test_mount_opt(ceph_sb_to_client(inode->i_sb),
-					RBYTES))
+		if (ceph_test_mount_opt(ceph_sb_to_client(sb), RBYTES)) {
 			stat->size = ci->i_rbytes;
-		else
+		} else if (ceph_snap(inode) == CEPH_SNAPDIR) {
+			struct ceph_inode_info *pci;
+			struct ceph_snap_realm *realm;
+			struct inode *parent;
+
+			parent = ceph_lookup_inode(sb, ceph_ino(inode));
+			if (!parent)
+				return PTR_ERR(parent);
+
+			pci = ceph_inode(parent);
+			spin_lock(&pci->i_ceph_lock);
+			realm = pci->i_snap_realm;
+			if (realm)
+				stat->size = realm->num_snaps;
+			else
+				stat->size = 0;
+			spin_unlock(&pci->i_ceph_lock);
+			iput(parent);
+		} else {
 			stat->size = ci->i_files + ci->i_subdirs;
+		}
 		stat->blocks = 0;
 		stat->blksize = 65536;
 		/*