read-only vblade storage

Reference: /n/atom/patch/applied/vbladero
Date: Thu Mar 13 15:13:42 CET 2014
Signed-off-by: quanstro@quansto.net

--- /sys/man/8/vblade	Thu Mar 13 15:13:28 2014
+++ /sys/man/8/vblade	Thu Mar 13 15:13:28 2014
@@ -4,7 +4,7 @@
 .SH SYNOPSIS
 .B vblade
 [
-.B -ir
+.B -iro
 ] [
 .B -s
 .I size
@@ -50,6 +50,9 @@
 Raw.  Do not use a configuration header.  This is useful when
 exporting a device or file not generally exported by
 .IR vblade .
+.TP
+.B -o
+Read only.  Do now allow writes to the backing store.
 .TP
 .BI -s " n"
 The exported target will have size
--- /sys/src/cmd/vblade/vblade.c	Thu Mar 13 15:13:28 2014
+++ /sys/src/cmd/vblade/vblade.c	Thu Mar 13 15:13:28 2014
@@ -36,6 +36,7 @@
 
 struct Conf {
 	int	iflag;
+	int	oflag;
 	int	flag;
 	int	shelf;
 	int	slot;
@@ -211,11 +212,14 @@
 }
 
 void
-checkfile(char *s, Vblade *vb, int iflag)
+checkfile(char *s, Vblade *vb, int iflag, int oflag)
 {
 	char *e;
 
-	vb->fd = open(s, ORDWR);
+	if(oflag)
+		vb->fd = open(s, OREAD);
+	else
+		vb->fd = open(s, ORDWR);
 	if(vb->fd == -1)
 		sysfatal("can't open backing store: %r");
 	if(iflag == 0 && (e = chkvblade(vb->fd, vb)))
@@ -751,7 +755,7 @@
 void
 usage(void)
 {
-	fprint(2, "vblade [-ir] [-s size] [-a shelf.slot] [-m mask] [-c config] [-e ether] file\n");
+	fprint(2, "vblade [-iro] [-s size] [-a shelf.slot] [-m mask] [-c config] [-e ether] file\n");
 	exits("usage");
 }
 
@@ -765,7 +769,7 @@
 		vblade->nmask = c->nmask;
 		vblade->mask = c->mask;
 	}
-	checkfile(file, vblade, c->iflag);
+	checkfile(file, vblade, c->iflag, c->oflag);
 
 	vblade->flag = c->flag;
 	if(c->shelf != -1){
@@ -801,7 +805,7 @@
 	for(;;){
 		if(nblade == nelem(vblade))
 			sysfatal("too many blades");
-		c = (Conf){0, 0, -1, -1, 0, 0, nil, nil};
+		c = (Conf){0, 0, 0, -1, -1, 0ull, 0, nil, nil};
 		lastc = 0;
 		ARGBEGIN{
 		case 'a':
@@ -842,6 +846,10 @@
 		case 's':
 			lastc = 's';
 			c.maxlba = sizetolba(getsize(EARGF(usage())));
+			break;
+		case 'o':
+			lastc = 'o';
+			c.oflag = 1;
 			break;
 		default:
 			lastc = '?';