NFSv4: Ensure we request the ordinary fileid when doing readdirplus

When readdir() returns a directory entry for the root of a mounted
filesystem, Linux follows the old convention of returning the inode
number of the covered directory (despite newer versions of POSIX declaring
that this is a bug).
To ensure this continues to work, the NFSv4 readdir implementation requests
the 'mounted-on-fileid' from the server.

However, readdirplus also needs to instantiate an inode for this entry, and
for that, we also need to request the real fileid as per this patch.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4xdr.c

@@ -1452,26 +1452,25 @@ static void encode_read(struct xdr_stream *xdr, const struct nfs_readargs *args,
 
 static void encode_readdir(struct xdr_stream *xdr, const struct nfs4_readdir_arg *readdir, struct rpc_rqst *req, struct compound_hdr *hdr)
 {
-	uint32_t attrs[2] = {0, 0};
+	uint32_t attrs[2] = {
+		FATTR4_WORD0_RDATTR_ERROR,
+		FATTR4_WORD1_MOUNTED_ON_FILEID,
+	};
 	uint32_t dircount = readdir->count >> 1;
 	__be32 *p;
 
 	if (readdir->plus) {
 		attrs[0] |= FATTR4_WORD0_TYPE|FATTR4_WORD0_CHANGE|FATTR4_WORD0_SIZE|
-			FATTR4_WORD0_FSID|FATTR4_WORD0_FILEHANDLE;
+			FATTR4_WORD0_FSID|FATTR4_WORD0_FILEHANDLE|FATTR4_WORD0_FILEID;
 		attrs[1] |= FATTR4_WORD1_MODE|FATTR4_WORD1_NUMLINKS|FATTR4_WORD1_OWNER|
 			FATTR4_WORD1_OWNER_GROUP|FATTR4_WORD1_RAWDEV|
 			FATTR4_WORD1_SPACE_USED|FATTR4_WORD1_TIME_ACCESS|
 			FATTR4_WORD1_TIME_METADATA|FATTR4_WORD1_TIME_MODIFY;
 		dircount >>= 1;
 	}
-	attrs[0] |= FATTR4_WORD0_RDATTR_ERROR|FATTR4_WORD0_FILEID;
-	attrs[1] |= FATTR4_WORD1_MOUNTED_ON_FILEID;
-	/* Switch to mounted_on_fileid if the server supports it */
-	if (readdir->bitmask[1] & FATTR4_WORD1_MOUNTED_ON_FILEID)
-		attrs[0] &= ~FATTR4_WORD0_FILEID;
-	else
-		attrs[1] &= ~FATTR4_WORD1_MOUNTED_ON_FILEID;
+	/* Use mounted_on_fileid only if the server supports it */
+	if (!(readdir->bitmask[1] & FATTR4_WORD1_MOUNTED_ON_FILEID))
+		attrs[0] |= FATTR4_WORD0_FILEID;
 
 	p = reserve_space(xdr, 12+NFS4_VERIFIER_SIZE+20);
 	*p++ = cpu_to_be32(OP_READDIR);
@@ -3140,7 +3139,7 @@ static int decode_attr_mounted_on_fileid(struct xdr_stream *xdr, uint32_t *bitma
 			goto out_overflow;
 		xdr_decode_hyper(p, fileid);
 		bitmap[1] &= ~FATTR4_WORD1_MOUNTED_ON_FILEID;
-		ret = NFS_ATTR_FATTR_FILEID;
+		ret = NFS_ATTR_FATTR_MOUNTED_ON_FILEID;
 	}
 	dprintk("%s: fileid=%Lu\n", __func__, (unsigned long long)*fileid);
 	return ret;
@@ -4002,7 +4001,6 @@ static int decode_getfattr_attrs(struct xdr_stream *xdr, uint32_t *bitmap,
 {
 	int status;
 	umode_t fmode = 0;
-	uint64_t fileid;
 	uint32_t type;
 
 	status = decode_attr_type(xdr, bitmap, &type);
@@ -4101,13 +4099,10 @@ static int decode_getfattr_attrs(struct xdr_stream *xdr, uint32_t *bitmap,
 		goto xdr_error;
 	fattr->valid |= status;
 
-	status = decode_attr_mounted_on_fileid(xdr, bitmap, &fileid);
+	status = decode_attr_mounted_on_fileid(xdr, bitmap, &fattr->mounted_on_fileid);
 	if (status < 0)
 		goto xdr_error;
-	if (status != 0 && !(fattr->valid & status)) {
-		fattr->fileid = fileid;
-		fattr->valid |= status;
-	}
+	fattr->valid |= status;
 
 xdr_error:
 	dprintk("%s: xdr returned %d\n", __func__, -status);
@@ -6411,7 +6406,9 @@ int nfs4_decode_dirent(struct xdr_stream *xdr, struct nfs_entry *entry,
 	if (decode_getfattr_attrs(xdr, bitmap, entry->fattr, entry->fh,
 					entry->server, 1) < 0)
 		goto out_overflow;
-	if (entry->fattr->valid & NFS_ATTR_FATTR_FILEID)
+	if (entry->fattr->valid & NFS_ATTR_FATTR_MOUNTED_ON_FILEID)
+		entry->ino = entry->fattr->mounted_on_fileid;
+	else if (entry->fattr->valid & NFS_ATTR_FATTR_FILEID)
 		entry->ino = entry->fattr->fileid;
 
 	entry->d_type = DT_UNKNOWN;

include/linux/nfs_xdr.h

@@ -50,6 +50,7 @@ struct nfs_fattr {
 	} du;
 	struct nfs_fsid		fsid;
 	__u64			fileid;
+	__u64			mounted_on_fileid;
 	struct timespec		atime;
 	struct timespec		mtime;
 	struct timespec		ctime;
@@ -83,6 +84,7 @@ struct nfs_fattr {
 #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 (NFS_ATTR_FATTR_TYPE \
 		| NFS_ATTR_FATTR_MODE \