add hack from sources for partfs.  we're using sdloop for this,
so this should not be necessary.  but it's not worth incompatability,
either.

Reference: /n/atom/patch/applied/partfshack
Date: Sat Mar  1 16:25:51 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/disk/partfs.c	Sat Mar  1 16:25:18 2014
+++ /sys/src/cmd/disk/partfs.c	Sat Mar  1 16:25:19 2014
@@ -107,6 +107,27 @@
 }
 
 static void
+addparts(char *buf)
+{
+	char *f[4], *p, *q;
+
+	/*
+	 * Use partitions passed from boot program,
+	 * e.g.
+	 *	sdC0part=dos 63 123123/plan9 123123 456456
+	 * This happens before /boot sets hostname so the
+	 * partitions will have the null-string for user.
+	 */
+	for(p = buf; p != nil; p = q){
+		if(q = strchr(p, '/'))
+			*q++ = '\0';
+		if(tokenize(p, f, nelem(f)) >= 3 &&
+		    addpart(f[0], strtoull(f[1], 0, 0), strtoull(f[2], 0, 0)) < 0)
+			fprint(2, "%s: addpart %s: %r\n", argv0, f[0]);
+	}
+}
+
+static void
 ctlwrite0(Req *r, char *msg, Cmdbuf *cb)
 {
 	vlong start, end;
@@ -253,12 +274,6 @@
 	return 0;
 }
 
-void*
-evommem(void *a, void *b, ulong n)
-{
-	return memmove(b, a, n);
-}
-
 int
 rdwrpart(Req *r)
 {
@@ -491,8 +506,8 @@
 void
 usage(void)
 {
-	fprint(2, "usage: %s [-Dr] [-d sdname] [-m mtpt] [-s srvname] diskimage\n",
-		argv0);
+	fprint(2, "usage: %s [-Dr] [-d sdname] [-m mtpt] [-p 9parts] "
+		"[-s srvname] diskimage\n", argv0);
 	fprint(2, "\tdefault mtpt is /dev\n");
 	exits("usage");
 }
@@ -501,11 +516,12 @@
 main(int argc, char **argv)
 {
 	int isdir;
-	char *file, *cname;
+	char *file, *cname, *parts;
 	Dir *dir;
 
 	quotefmtinstall();
 	time0 = time(0);
+	parts = nil;
 
 	ARGBEGIN{
 	case 'D':
@@ -517,6 +533,9 @@
 	case 'm':
 		mtpt = EARGF(usage());
 		break;
+	case 'p':
+		parts = EARGF(usage());
+		break;
 	case 'r':
 		rdonly = 1;
 		break;
@@ -556,6 +575,12 @@
 	tab[0].name = estrdup9p("data");
 	tab[0].mode = 0666;
 	tab[0].length = nsect;
+
+	/*
+	 * hack for booting from usb: add 9load partitions.
+	 */
+	if(parts != nil)
+		addparts(parts);
 
 	postmountsrv(&fs, srvname, mtpt, MBEFORE);
 	exits(nil);