NFS: Introduce NFS_ATTR_FATTR_V4_LOCATIONS

The Linux NFS client must distinguish between referral events (which
it currently supports) and migration events (which it does not yet
support).

In both types of events, an fs_locations array is returned.  But upper
layers, not the XDR layer, should make the distinction between a
referral and a migration.  There really isn't a way for an XDR decoder
function to distinguish the two, in general.

Slightly adjust the FATTR flags returned by decode_fs_locations()
to set NFS_ATTR_FATTR_V4_LOCATIONS only if a non-empty locations
array was returned from the server.  Then have logic in nfs4proc.c
distinguish whether the locations array is for a referral or
something else.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -79,6 +79,7 @@ static int _nfs4_proc_open(struct nfs4_opendata *data);
 static int _nfs4_recover_proc_open(struct nfs4_opendata *data);
 static int nfs4_do_fsinfo(struct nfs_server *, struct nfs_fh *, struct nfs_fsinfo *);
 static int nfs4_async_handle_error(struct rpc_task *, const struct nfs_server *, struct nfs4_state *);
+static void nfs_fixup_referral_attributes(struct nfs_fattr *fattr);
 static int _nfs4_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle, struct nfs_fattr *fattr);
 static int nfs4_do_setattr(struct inode *inode, struct rpc_cred *cred,
 			    struct nfs_fattr *fattr, struct iattr *sattr,
@@ -2340,7 +2341,6 @@ static int nfs4_proc_get_root(struct nfs_server *server, struct nfs_fh *fhandle,
 	return nfs4_map_errors(status);
 }
 
-static void nfs_fixup_referral_attributes(struct nfs_fattr *fattr);
 /*
  * Get locations and (maybe) other attributes of a referral.
  * Note that we'll actually follow the referral later when
@@ -4797,11 +4797,11 @@ static void nfs_fixup_referral_attributes(struct nfs_fattr *fattr)
 	if (!(((fattr->valid & NFS_ATTR_FATTR_MOUNTED_ON_FILEID) ||
 	       (fattr->valid & NFS_ATTR_FATTR_FILEID)) &&
 	      (fattr->valid & NFS_ATTR_FATTR_FSID) &&
-	      (fattr->valid & NFS_ATTR_FATTR_V4_REFERRAL)))
+	      (fattr->valid & NFS_ATTR_FATTR_V4_LOCATIONS)))
 		return;
 
 	fattr->valid |= NFS_ATTR_FATTR_TYPE | NFS_ATTR_FATTR_MODE |
-		NFS_ATTR_FATTR_NLINK;
+		NFS_ATTR_FATTR_NLINK | NFS_ATTR_FATTR_V4_REFERRAL;
 	fattr->mode = S_IFDIR | S_IRUGO | S_IXUGO;
 	fattr->nlink = 2;
 }

fs/nfs/nfs4xdr.c

@@ -3660,7 +3660,7 @@ static int decode_attr_fs_locations(struct xdr_stream *xdr, uint32_t *bitmap, st
 			res->nlocations++;
 	}
 	if (res->nlocations != 0)
-		status = NFS_ATTR_FATTR_V4_REFERRAL;
+		status = NFS_ATTR_FATTR_V4_LOCATIONS;
 out:
 	dprintk("%s: fs_locations done, error = %d\n", __func__, status);
 	return status;

include/linux/nfs_xdr.h

@@ -88,11 +88,12 @@ struct nfs_fattr {
 #define NFS_ATTR_FATTR_PRECTIME		(1U << 16)
 #define NFS_ATTR_FATTR_CHANGE		(1U << 17)
 #define NFS_ATTR_FATTR_PRECHANGE	(1U << 18)
-#define NFS_ATTR_FATTR_V4_REFERRAL	(1U << 19)	/* NFSv4 referral */
-#define NFS_ATTR_FATTR_MOUNTPOINT	(1U << 20)	/* Treat as mountpoint */
-#define NFS_ATTR_FATTR_MOUNTED_ON_FILEID		(1U << 21)
-#define NFS_ATTR_FATTR_OWNER_NAME	(1U << 22)
-#define NFS_ATTR_FATTR_GROUP_NAME	(1U << 23)
+#define NFS_ATTR_FATTR_V4_LOCATIONS	(1U << 19)
+#define NFS_ATTR_FATTR_V4_REFERRAL	(1U << 20)
+#define NFS_ATTR_FATTR_MOUNTPOINT	(1U << 21)
+#define NFS_ATTR_FATTR_MOUNTED_ON_FILEID (1U << 22)
+#define NFS_ATTR_FATTR_OWNER_NAME	(1U << 23)
+#define NFS_ATTR_FATTR_GROUP_NAME	(1U << 24)
 
 #define NFS_ATTR_FATTR (NFS_ATTR_FATTR_TYPE \
 		| NFS_ATTR_FATTR_MODE \