ceph: add a new vxattr to return auth mds for an inode

Add a new vxattr that shows what MDS is authoritative for an inode (if
we happen to have auth caps). If we don't have an auth cap for the inode
then just return -1.

URL: https://tracker.ceph.com/issues/1276Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Luis Henriques <lhenriques@suse.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/xattr.c

@@ -340,6 +340,18 @@ static ssize_t ceph_vxattrcb_caps(struct ceph_inode_info *ci, char *val,
 			      ceph_cap_string(issued), issued);
 }
 
+static ssize_t ceph_vxattrcb_auth_mds(struct ceph_inode_info *ci,
+				       char *val, size_t size)
+{
+	int ret;
+
+	spin_lock(&ci->i_ceph_lock);
+	ret = ceph_fmt_xattr(val, size, "%d",
+			     ci->i_auth_cap ? ci->i_auth_cap->session->s_mds : -1);
+	spin_unlock(&ci->i_ceph_lock);
+	return ret;
+}
+
 #define CEPH_XATTR_NAME(_type, _name)	XATTR_CEPH_PREFIX #_type "." #_name
 #define CEPH_XATTR_NAME2(_type, _name, _name2)	\
 	XATTR_CEPH_PREFIX #_type "." #_name "." #_name2
@@ -473,6 +485,13 @@ static struct ceph_vxattr ceph_common_vxattrs[] = {
 		.exists_cb = NULL,
 		.flags = VXATTR_FLAG_READONLY,
 	},
+	{
+		.name = "ceph.auth_mds",
+		.name_size = sizeof("ceph.auth_mds"),
+		.getxattr_cb = ceph_vxattrcb_auth_mds,
+		.exists_cb = NULL,
+		.flags = VXATTR_FLAG_READONLY,
+	},
 	{ .name = NULL, 0 }	/* Required table terminator */
 };