srv: add -n flag to reject auth by clients

man/man4/srv.4

@@ -4,7 +4,7 @@ srv, 9fs \- start network file service
 .SH SYNOPSIS
 .B srv
 [
-.B -a
+.B -an
 ]
 [
 .B -k
@@ -37,6 +37,14 @@ to post a pre-authenticated connection to the file system
 (by default, the empty string;
 see
 .IR attach (9p)).
+.PP
+The 
+.B -n
+option causes 
+.I srv
+to reject authentication attempts by clients,
+useful if the remote server is known not to require authentication.
+.PP
 .I Srv
 authenticates over the 9P connection to establish a valid auth fid.
 .IR Keypattern ,

src/cmd/srv.c

@@ -41,6 +41,9 @@ threadmain(int argc, char **argv)
 	case 'a':
 		doauth = 1;
 		break;
+	case 'n':
+		doauth = -1;
+		break;
 	case 'k':
 		keypattern = EARGF(usage());
 		break;
@@ -55,7 +58,7 @@ threadmain(int argc, char **argv)
 	if((fd = dial(addr, nil, nil, nil)) < 0)
 		sysfatal("dial %s: %r", addr);
 
-	if(doauth)
+	if(doauth > 0)
 		xauth();
 
 	if(argc == 2)
@@ -216,7 +219,7 @@ post9pservice(int fd, char *name)
 		dup(fd, 1);
 		for(i=3; i<20; i++)
 			close(i);
-		if(doauth)
+		if(doauth > 0)
 			execlp("9pserve", "9pserve", "-u",
 				"-M",
 					smprint("%d", msize),
@@ -225,7 +228,8 @@ post9pservice(int fd, char *name)
 					smprint("%d", afid),
 				s, (char*)0);
 		else
-			execlp("9pserve", "9pserve", "-u", s, (char*)0);
+			execlp("9pserve", "9pserve",
+				doauth < 0 ? "-nu" : "-u", s, (char*)0);
 		fprint(2, "exec 9pserve: %r\n");
 		_exits("exec");
 	default: