add help text and update README with similar info

README.md

@@ -78,13 +78,20 @@ or expose a service on the network (uses `9pserve` to support multiple users and
 ./xrxs-srv.sh start
 ```
 
+Add the `-d` option to the above command to enable 9p debugging output.
+
 Similarly, you can stop the service with:
 
 ```
 ./xrxs-srv.sh stop
 ```
 
-You can add `-d` to either the `xrxs` command line or the `xrxs-srv.sh` command line to enable chatty `9p` debug output.
+The executable itself supports the following options, one of which is required (no options prints the help text):
+
+  * `-m MOUNTPOINT`: mount the 9p filesystem locally at MOUNTPOINT
+  * `-s SOCKET`: serve the 9p filesystem over a socket named SOCKET
+  * `-v`: print the version information
+  * `-h | --help`: show the help text
 
 ### client
 

server/xrxs.c

@@ -25,6 +25,18 @@ static Tree* tree;
 
 static UserInfo users_table[MAX_USERS];
 
+void helpme(char* arg0) {
+  printf("usage: %s [-m MOUNTPOINT | -s SOCKET | -v | -h|--help]\n", arg0);
+  printf("Serve xrxs game infrastructure over 9p.\n\n");
+
+  printf("  -m MOUNTPOINT: mount the 9p filesystem locally at MOUNTPOINT\n");
+  printf("  -s SOCKET: create a socket for the 9p filesystem with the "
+         "namespace SOCKET\n");
+  printf("  -v: print version information\n");
+  printf("  -h | --help: print this help text\n\n");
+  threadexits(0);
+}
+
 void xrxs_attach(Req* r) {
   /* As it is, once the user detaches, they will stay in the table
    * until the server restarts. We have to figure out some way
@@ -626,6 +638,10 @@ void threadmain(int argc, char* argv[]) {
       printf("xrxs v%s\n", version);
       threadexits(0);
     }
+
+    if (scmp(argv[i], "-h") || scmp(argv[i], "--help")) {
+      helpme(argv[0]);
+    }
   }
 
   fs.foreground = 1;
@@ -676,6 +692,6 @@ void threadmain(int argc, char* argv[]) {
     threadpostmountsrv(&fs, usocket, mtpt, MREPL | MCREATE);
     threadexits(0);
   } else {
-    srv(&fs);
+    helpme(argv[0]);
   }
 }