ceph: support getting ceph.dir.rsnaps vxattr

Add support for grabbing the rsnaps value out of the inode info in
traces, and exposing that via ceph.dir.rsnaps xattr.

Signed-off-by: Yanhu Cao <gmayyyha@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
index 02f59bc..1242db8 100644
--- a/fs/ceph/xattr.c
+++ b/fs/ceph/xattr.c
@@ -233,6 +233,12 @@ static ssize_t ceph_vxattrcb_dir_rsubdirs(struct ceph_inode_info *ci, char *val,
 	return ceph_fmt_xattr(val, size, "%lld", ci->i_rsubdirs);
 }
 
+static ssize_t ceph_vxattrcb_dir_rsnaps(struct ceph_inode_info *ci, char *val,
+					  size_t size)
+{
+	return ceph_fmt_xattr(val, size, "%lld", ci->i_rsnaps);
+}
+
 static ssize_t ceph_vxattrcb_dir_rbytes(struct ceph_inode_info *ci, char *val,
 					size_t size)
 {
@@ -384,6 +390,7 @@ static struct ceph_vxattr ceph_dir_vxattrs[] = {
 	XATTR_RSTAT_FIELD(dir, rentries),
 	XATTR_RSTAT_FIELD(dir, rfiles),
 	XATTR_RSTAT_FIELD(dir, rsubdirs),
+	XATTR_RSTAT_FIELD(dir, rsnaps),
 	XATTR_RSTAT_FIELD(dir, rbytes),
 	XATTR_RSTAT_FIELD(dir, rctime),
 	{