From: Romano <me+unobe@fallglow.com>
Date: Fri, 17 May 2024 08:08:34 +0000
Subject: [PATCH] ramfs: document usage and provide clearer usage errors

---
diff b1e897ae44d25909ebc99992a32a93ac019b98b1 6d02b515abae742baf37cde7817ebc34cd0656d1
--- a/sys/man/4/ramfs
+++ b/sys/man/4/ramfs
@@ -4,7 +4,7 @@
 .SH SYNOPSIS
 .B ramfs
 [
-.B -Dipsu
+.B -Dipsubac
 ]
 [
 .B -m
@@ -15,23 +15,43 @@
 .I srvname
 ]
 .SH DESCRIPTION
+.PP
 .I Ramfs
-starts a process that mounts itself (see
-.IR bind (2))
-on
-.I mountpoint
-(default
-.BR /tmp ).
+implements a file tree which keeps all files in memory.
+Initially the file tree is empty.
+.PP
 The
 .I ramfs
-process implements a file tree rooted at
-.IR dir ,
-keeping all files in memory.
-Initially the file tree is empty.
+process mounts the
+.IR mountpoint (or
+.B /tmp ,
+if not provided)
+with the mount flags
+.B MREPL and
+.B MCREATE .
+The mount flags can be set explicitly
+using
+.B -b ,
+.B -a , and
+.B -c ,
+corresponding respectively to the flags
+.B MBEFORE ,
+.B MAFTER , or
+.B MCREATE (see
+.IR bind(2)).
 .PP
 The
+.B -p
+flag causes
+.I ramfs
+to make its memory `private'
+(see
+.IR proc (3))
+so that its files are not accessible through the debugging interface.
+.PP
+The
 .B -D
-option enables a trace of general debugging messages.
+flag enables a trace of general debugging messages.
 .PP
 The
 .B -i
@@ -38,7 +58,8 @@
 flag tells
 .I ramfs
 to use file descriptors 0 and 1 for its communication channel
-rather than create a pipe.
+rather than create a pipe or mount at
+.IR mountpoint .
 This makes it possible to use
 .I ramfs
 as a file server on a remote machine: the file descriptors 0
@@ -47,15 +68,6 @@
 to the client machine.
 .PP
 The
-.B -p
-flag causes
-.I ramfs
-to make its memory `private'
-(see
-.IR proc (3))
-so that its files are not accessible through the debugging interface.
-.PP
-The
 .B -s
 .RB ( -S )
 flag causes
@@ -62,17 +74,26 @@
 .I ramfs
 to post its channel on
 .B /srv/ramfs
-.RB ( /srv/ \fIsrvname\fR)
-rather than mounting it on
-.IR mountpoint ,
+.RB ( /srv/ \fIsrvname\fR) ,
 enabling multiple clients to access its files.
-However, it does not authenticate its clients and its
+The flag also causes
+.I ramfs
+to not use the default
+.IR mountpoint
+.B /tmp ,
+however it will use the mountpoint
+.IR mountpoint
+explicitly set using the
+.B -m
+flag.
+.I Ramfs
+does not authenticate its clients and its
 implementation of groups is simplistic, so
 it should not be used for precious data.
 .PP
 The
 .B -u
-option permits
+flag permits
 .I ramfs
 to consume as much memory as needed;
 without it,
@@ -86,4 +107,5 @@
 .SH SOURCE
 .B /sys/src/cmd/ramfs.c
 .SH "SEE ALSO"
-.IR bind (2)
+.IR bind (2) ,
+.IR proc (3)
--- a/sys/src/cmd/ramfs.c
+++ b/sys/src/cmd/ramfs.c
@@ -455,27 +455,40 @@
 {
 	char *srvname = nil;
 	char *mtpt = "/tmp";
-	int mountflags, stdio;
+	int marg, mountflags, stdio;
 
 	fs.tree = alloctree(nil, nil, DMDIR|0777, fsdestroyfile);
 
-	mountflags = stdio = 0;
+	marg = mountflags = stdio = 0;
 	ARGBEGIN{
 	case 'D':
 		chatty9p++;
 		break;
 	case 's':
+		if(stdio)
+			sysfatal("-s cannot be used with -i flag");
 		srvname = "ramfs";
-		mtpt = nil;
+		if(!marg)
+			mtpt = nil;
 		break;
 	case 'S':
+		if(stdio)
+			sysfatal("-S cannot be used with -i flag");
+		if(srvname)
+			sysfatal("-s cannot be used with -S");
 		srvname = EARGF(usage());
-		mtpt = nil;
+		if(!marg)
+			mtpt = nil;
 		break;
 	case 'm':
+		if(stdio)
+			sysfatal("-m cannot be used with -i flag");
 		mtpt = EARGF(usage());
+		marg = 1;
 		break;
 	case 'i':
+		if(srvname || marg)
+			sysfatal("-i cannot be used with -s, -S, or -m flag");
 		stdio = 1;
 		break;
 	case 'p':
@@ -500,14 +513,14 @@
 		usage();
 
 	if(stdio){
+		if(mountflags)
+			perror("mount flags ignored when using -i");
+
 		fs.infd = 0;
 		fs.outfd = 1;
 		srv(&fs);
 		exits(0);
 	}
-
-	if(srvname == nil && mtpt == nil)
-		sysfatal("must specify -S, or -m option");
 
 	if(mountflags == 0)
 		mountflags = MREPL | MCREATE;