[PATCH] PATCH 2 of 4 : knfsd : Allow exporting of deviceless filesystems if fsid= given

Previously we could only export FS_REQUIRES_DEV filesystems
as we need a devno to put in the filehandle.
Now that we have fsid= (NFSEXP_FSID) we don't need a devno
to put in the filehandle so we can relax this requirement.

fs/nfsd/export.c

@@ -304,9 +304,21 @@ exp_export(struct nfsctl_export *nxp)
 		goto finish;
 
 	err = -EINVAL;
-	if (!(inode->i_sb->s_type->fs_flags & FS_REQUIRES_DEV) ||
-	    (inode->i_sb->s_op->read_inode == NULL
-	     && inode->i_sb->s_op->fh_to_dentry == NULL)) {
+	/* There are two requirements on a filesystem to be exportable.
+	 * 1:  We must be able to identify the filesystem from a number.
+	 *       either a device number (so FS_REQUIRES_DEV needed)
+	 *       or an FSID number (so NFSEXP_FSID needed).
+	 * 2:  We must be able to find an inode from a filehandle.
+	 *       either using fh_to_dentry (prefered)
+	 *       or using read_inode (the hack).
+	 */
+	if (((inode->i_sb->s_type->fs_flags & FS_REQUIRES_DEV)
+	      || (nxp->ex_flags & NFSEXP_FSID))
+	    &&
+	    (inode->i_sb->s_op->read_inode
+	     || inode->i_sb->s_op->fh_to_dentry)) 
+		/* Ok, we can export it */;
+	else {
 		dprintk("exp_export: export of invalid fs type.\n");
 		goto finish;
 	}