noticed during a vbox trial.

it may be that usbd will not start for legit reasons, such as no hubs.
don't panic, keep going.

Reference: /n/atom/patch/applied/nixnousb
Date: Tue Apr  8 17:19:31 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/boot/boot.c	Tue Apr  8 17:17:58 2014
+++ /sys/src/nix/boot/boot.c	Tue Apr  8 17:17:59 2014
@@ -293,7 +293,7 @@
 
 	if(access("#u/usb/ctl", 0) >= 0 && bind("#u", "/dev", MAFTER) >= 0 &&
 	    access(usbd, AEXIST) >= 0){
-		run(usbd, "-m", "/dev", nil);
+		run(0, usbd, "-m", "/dev", nil);	/* may fail if no hubs */
 		s = getenv("drive0");
 		if(s != nil && strstr(s, " usb=") != nil)
 			usbbootdrive();
--- /sys/src/nix/boot/boot.h	Tue Apr  8 17:18:00 2014
+++ /sys/src/nix/boot/boot.h	Tue Apr  8 17:18:01 2014
@@ -34,7 +34,7 @@
 extern void	key(int, Method*);
 extern int	outin(char*, char*, int);
 extern int	readfile(char*, char*, int);
-extern void	run(char *file, ...);
+extern void	run(int, char*, ...);
 extern void	setenv(char*, char*);
 extern void	settime(int, int, char*);
 extern void	srvcreate(char*, int);
--- /sys/src/nix/boot/bootauth.c	Tue Apr  8 17:18:02 2014
+++ /sys/src/nix/boot/bootauth.c	Tue Apr  8 17:18:02 2014
@@ -49,9 +49,6 @@
 	/* wait for agent to really be there */
 	while(access("/mnt/factotum", 0) < 0)
 		sleep(250);
-
-	if(cpuflag)
-		return;
 }
 
 static void
--- /sys/src/nix/boot/local.c	Tue Apr  8 17:18:03 2014
+++ /sys/src/nix/boot/local.c	Tue Apr  8 17:18:04 2014
@@ -118,7 +118,7 @@
 }
 
 void
-run(char *file, ...)
+run(int must, char *file, ...)
 {
 	int i, pid;
 
@@ -131,7 +131,7 @@
 	default:
 		while ((i = waitpid()) != pid && i != -1)
 			;
-		if(i == -1)
+		if(must && i == -1)
 			fatal(smprint("wait failed running %s", file));
 	}
 }
@@ -212,7 +212,7 @@
 				f[2] = "tcp!127.1!8000";
 			}
 			configloopback();
-			run("/boot/venti", "-c", f[0], "-a", f[1], "-h", f[2], nil);
+			run(1, "/boot/venti", "-c", f[0], "-a", f[1], "-h", f[2], nil);
 			/*
 			 * If the announce address is tcp!*!foo, then set
 			 * $venti to tcp!127.1!foo instead, which is actually dialable.
@@ -233,7 +233,7 @@
 
 	/* start fossil */
 	print("fossil(%s)...", partition);
-	run("/boot/fossil", "-f", partition, "-c", "srv -A fboot", "-c", "srv -p fscons", nil);
+	run(1, "/boot/fossil", "-f", partition, "-c", "srv -A fboot", "-c", "srv -p fscons", nil);
 	fd = open("#s/fboot", ORDWR);
 	if(fd < 0){
 		print("open #s/fboot: %r\n");