NFS: Add a boot parameter to disable 64 bit inode numbers

This boot parameter will allow legacy 32-bit applications which call stat()
to continue to function even if the NFSv3/v4 server uses 64-bit inode
numbers.

Signed-off-by: Trond Myklebust <[e-mail]>

Documentation/kernel-parameters.txt

···
 			[NFS] set the maximum lifetime for idmapper cache
 			entries.
 
+	nfs.enable_ino64=
+			[NFS] enable 64-bit inode numbers.
+			If zero, the NFS client will fake up a 32-bit inode
+			number for the readdir() and stat() syscalls instead
+			of returning the full 64-bit number.
+			The default is to return 64-bit inode numbers.
+
 	nmi_watchdog=	[KNL,BUGS=X86-32] Debugging features for SMP kernels
 
 	no387		[BUGS=X86-32] Tells the kernel to use the 387 maths

fs/nfs/dir.c

···
 		}
 
 		res = filldir(dirent, entry->name, entry->len, 
-			      file->f_pos, fileid, d_type);
+			      file->f_pos, nfs_compat_user_ino64(fileid),
+			      d_type);
 		if (res < 0)
 			break;
 		file->f_pos++;

fs/nfs/inode.c

···
 
 #define NFSDBG_FACILITY		NFSDBG_VFS
 
+#define NFS_64_BIT_INODE_NUMBERS_ENABLED	1
+
+/* Default is to see 64-bit inode numbers */
+static int enable_ino64 = NFS_64_BIT_INODE_NUMBERS_ENABLED;
+
 static void nfs_invalidate_inode(struct inode *);
 static int nfs_update_inode(struct inode *, struct nfs_fattr *);
 
···
 nfs_fattr_to_ino_t(struct nfs_fattr *fattr)
 {
 	return nfs_fileid_to_ino_t(fattr->fileid);
+}
+
+/**
+ * nfs_compat_user_ino64 - returns the user-visible inode number
+ * @fileid: 64-bit fileid
+ *
+ * This function returns a 32-bit inode number if the boot parameter
+ * nfs.enable_ino64 is zero.
+ */
+u64 nfs_compat_user_ino64(u64 fileid)
+{
+	int ino;
+
+	if (enable_ino64)
+		return fileid;
+	ino = fileid;
+	if (sizeof(ino) < sizeof(fileid))
+		ino ^= fileid >> (sizeof(fileid)-sizeof(ino)) * 8;
+	return ino;
 }
 
 int nfs_write_inode(struct inode *inode, int sync)
···
 		err = nfs_revalidate_inode(NFS_SERVER(inode), inode);
 	if (!err) {
 		generic_fillattr(inode, stat);
-		stat->ino = NFS_FILEID(inode);
+		stat->ino = nfs_compat_user_ino64(NFS_FILEID(inode));
 	}
 	return err;
 }
···
 /* Not quite true; I just maintain it */
 MODULE_AUTHOR("Olaf Kirch <[e-mail]>");
 MODULE_LICENSE("GPL");
+module_param(enable_ino64, bool, 0644);
 
 module_init(init_nfs_fs)
 module_exit(exit_nfs_fs)

include/linux/nfs_fs.h

···
 extern struct nfs_open_context *get_nfs_open_context(struct nfs_open_context *ctx);
 extern void put_nfs_open_context(struct nfs_open_context *ctx);
 extern struct nfs_open_context *nfs_find_open_context(struct inode *inode, struct rpc_cred *cred, int mode);
+extern u64 nfs_compat_user_ino64(u64 fileid);
 
 /* linux/net/ipv4/ipconfig.c: trims ip addr off front of name, too. */
 extern __be32 root_nfs_parse_addr(char *name); /*__init*/