[PATCH] return to old errno choice in mkdir() et.al.

In case when both EEXIST and EROFS would apply we used to
return the former in mkdir(2) and friends.  Lest anyone suspects
us of being consistent, in the same situation knfsd gave clients
nfs_erofs...

	ro-bind series had switched the syscall side of things to
returning -EROFS and immediately broke an application - namely,
mkdir -p.  Patch restores the original behaviour...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -2003,18 +2003,22 @@ struct dentry *lookup_create(struct nameidata *nd, int is_dir)
 	if (IS_ERR(dentry))
 		goto fail;
 
+	if (dentry->d_inode)
+		goto eexist;
 	/*
 	 * Special case - lookup gave negative, but... we had foo/bar/
 	 * From the vfs_mknod() POV we just have a negative dentry -
 	 * all is fine. Let's be bastards - you had / on the end, you've
 	 * been asking for (non-existent) directory. -ENOENT for you.
 	 */
-	if (!is_dir && nd->last.name[nd->last.len] && !dentry->d_inode)
-		goto enoent;
+	if (unlikely(!is_dir && nd->last.name[nd->last.len])) {
+		dput(dentry);
+		dentry = ERR_PTR(-ENOENT);
+	}
 	return dentry;
-enoent:
+eexist:
 	dput(dentry);
-	dentry = ERR_PTR(-ENOENT);
+	dentry = ERR_PTR(-EEXIST);
 fail:
 	return dentry;
 }