[PATCH] knfsd: Add server-side support for the nfsv4 mounted_on_fileid attribute.

From: NeilBrown <neilb@cse.unsw.edu.au>

fs/nfsd/nfs4xdr.c

@@ -1588,7 +1588,18 @@ nfsd4_encode_fattr(struct svc_fh *fhp, struct svc_export *exp,
 		WRITE32(stat.mtime.tv_sec);
 		WRITE32(stat.mtime.tv_nsec);
 	}
+	if (bmval1 & FATTR4_WORD1_MOUNTED_ON_FILEID) {
+		struct dentry *mnt_pnt, *mnt_root;
 
+		if ((buflen -= 8) < 0)
+                	goto out_resource;
+		mnt_root = exp->ex_mnt->mnt_root;
+		if (mnt_root->d_inode == dentry->d_inode) {
+			mnt_pnt = exp->ex_mnt->mnt_mountpoint;
+			WRITE64((u64) mnt_pnt->d_inode->i_ino);
+		} else
+                	WRITE64((u64) stat.ino);
+	}
 	*attrlenp = htonl((char *)p - (char *)attrlenp - 4);
 	*countp = p - buffer;
 	status = nfs_ok;

include/linux/nfs4.h

@@ -274,6 +274,7 @@ enum lock_type4 {
 #define FATTR4_WORD1_TIME_METADATA      (1 << 20)
 #define FATTR4_WORD1_TIME_MODIFY        (1 << 21)
 #define FATTR4_WORD1_TIME_MODIFY_SET    (1 << 22)
+#define FATTR4_WORD1_MOUNTED_ON_FILEID  (1 << 23)
 
 #define NFSPROC4_NULL 0
 #define NFSPROC4_COMPOUND 1

include/linux/nfsd/nfsd.h

@@ -278,7 +278,7 @@ static inline int is_fsid(struct svc_fh *fh, struct knfsd_fh *reffh)
  | FATTR4_WORD1_SPACE_AVAIL     | FATTR4_WORD1_SPACE_FREE   | FATTR4_WORD1_SPACE_TOTAL      \
  | FATTR4_WORD1_SPACE_USED      | FATTR4_WORD1_TIME_ACCESS  | FATTR4_WORD1_TIME_ACCESS_SET  \
  | FATTR4_WORD1_TIME_CREATE     | FATTR4_WORD1_TIME_DELTA   | FATTR4_WORD1_TIME_METADATA    \
- | FATTR4_WORD1_TIME_MODIFY     | FATTR4_WORD1_TIME_MODIFY_SET)
+ | FATTR4_WORD1_TIME_MODIFY     | FATTR4_WORD1_TIME_MODIFY_SET | FATTR4_WORD1_MOUNTED_ON_FILEID)
 
 /* These will return ERR_INVAL if specified in GETATTR or READDIR. */
 #define NFSD_WRITEONLY_ATTRS_WORD1							    \