nfsd: clean up fh_auth usage

Use fh_fsid when reffering to the fsid part of the filehandle. The
variable length auth field envisioned in nfsfh wasn't ever implemented.
Also clean up some lose ends around this and document the file handle
format better.

Btw, why do we even export nfsfh.h to userspace? The file handle very
much is kernel private, and nothing in nfs-utils include the header
either.

Signed-off-by: Christoph Hellwig <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

fs/nfsd/nfsfh.c

···
 		data_left -= len;
 		if (data_left < 0)
 			return error;
-		exp = rqst_exp_find(rqstp, fh->fh_fsid_type, fh->fh_auth);
-		fid = (struct fid *)(fh->fh_auth + len);
+		exp = rqst_exp_find(rqstp, fh->fh_fsid_type, fh->fh_fsid);
+		fid = (struct fid *)(fh->fh_fsid + len);
 	} else {
 		__u32 tfh[2];
 		dev_t xdev;
···
 {
 	if (dentry != exp->ex_path.dentry) {
 		struct fid *fid = (struct fid *)
-			(fhp->fh_handle.fh_auth + fhp->fh_handle.fh_size/4 - 1);
+			(fhp->fh_handle.fh_fsid + fhp->fh_handle.fh_size/4 - 1);
 		int maxsize = (fhp->fh_maxsize - fhp->fh_handle.fh_size)/4;
 		int subtreecheck = !(exp->ex_flags & NFSEXP_NOSUBTREECHECK);
 
···
 	 */
 
 	struct inode * inode = dentry->d_inode;
-	__u32 *datap;
 	dev_t ex_dev = exp_sb(exp)->s_dev;
 
 	dprintk("nfsd: fh_compose(exp %02x:%02x/%ld %pd2, ino=%ld)\n",
···
 		if (inode)
 			_fh_update_old(dentry, exp, &fhp->fh_handle);
 	} else {
-		int len;
+		fhp->fh_handle.fh_size =
+			key_len(fhp->fh_handle.fh_fsid_type) + 4;
 		fhp->fh_handle.fh_auth_type = 0;
-		datap = fhp->fh_handle.fh_auth+0;
-		mk_fsid(fhp->fh_handle.fh_fsid_type, datap, ex_dev,
+
+		mk_fsid(fhp->fh_handle.fh_fsid_type,
+			fhp->fh_handle.fh_fsid,
+			ex_dev,
 			exp->ex_path.dentry->d_inode->i_ino,
 			exp->ex_fsid, exp->ex_uuid);
-
-		len = key_len(fhp->fh_handle.fh_fsid_type);
-		datap += len/4;
-		fhp->fh_handle.fh_size = 4 + len;
 
 		if (inode)
 			_fh_update(fhp, exp, dentry);

include/uapi/linux/nfsd/nfsfh.h

···
 /*
- * include/linux/nfsd/nfsfh.h
- *
  * This file describes the layout of the file handles as passed
  * over the wire.
- *
- * Earlier versions of knfsd used to sign file handles using keyed MD5
- * or SHA. I've removed this code, because it doesn't give you more
- * security than blocking external access to port 2049 on your firewall.
  *
  * Copyright (C) 1995, 1996, 1997 Olaf Kirch <[e-mail]>
  */
···
 };
 
 /*
- * This is the new flexible, extensible style NFSv2/v3 file handle.
+ * This is the new flexible, extensible style NFSv2/v3/v4 file handle.
  * by Neil Brown <[e-mail]> - March 2000
  *
  * The file handle starts with a sequence of four-byte words.
···
  *
  * All four-byte values are in host-byte-order.
  *
- * The auth_type field specifies how the filehandle can be authenticated
- * This might allow a file to be confirmed to be in a writable part of a
- * filetree without checking the path from it up to the root.
- * Current values:
- *     0  - No authentication.  fb_auth is 0 bytes long
- * Possible future values:
- *     1  - 4 bytes taken from MD5 hash of the remainer of the file handle
- *          prefixed by a secret and with the important export flags.
+ * The auth_type field is deprecated and must be set to 0.
  *
  * The fsid_type identifies how the filesystem (or export point) is
  *    encoded.
···
  *     7  - 8 byte inode number and 16 byte uuid
  *
  * The fileid_type identified how the file within the filesystem is encoded.
- * This is (will be) passed to, and set by, the underlying filesystem if it supports
- * filehandle operations.  The filesystem must not use the value '0' or '0xff' and may
- * only use the values 1 and 2 as defined below:
- *  Current values:
- *    0   - The root, or export point, of the filesystem.  fb_fileid is 0 bytes.
- *    1   - 32bit inode number, 32 bit generation number.
- *    2   - 32bit inode number, 32 bit generation number, 32 bit parent directory inode number.
- *
+ *   The values for this field are filesystem specific, exccept that
+ *   filesystems must not use the values '0' or '0xff'. 'See enum fid_type'
+ *   in include/linux/exportfs.h for currently registered values.
  */
 struct nfs_fhbase_new {
 	__u8		fb_version;	/* == 1, even => nfs_fhbase_old */
···
 #define	fh_fsid_type		fh_base.fh_new.fb_fsid_type
 #define	fh_auth_type		fh_base.fh_new.fb_auth_type
 #define	fh_fileid_type		fh_base.fh_new.fb_fileid_type
-#define	fh_auth			fh_base.fh_new.fb_auth
 #define	fh_fsid			fh_base.fh_new.fb_auth
 
-
+/* Do not use, provided for userspace compatiblity. */
+#define	fh_auth			fh_base.fh_new.fb_auth
 
 #endif /* _UAPI_LINUX_NFSD_FH_H */