Index: kern_subr.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_subr.c,v
retrieving revision 1.230
diff -p -u -r1.230 kern_subr.c
--- kern_subr.c	19 Mar 2022 13:51:35 -0000	1.230
+++ kern_subr.c	15 Jan 2023 08:22:39 -0000
@@ -174,6 +174,13 @@ uint64_t booted_nblks;
 char *bootspec;
 
 /*
+ * Time to wait for a specified boot device to appear.
+ */
+#ifndef ROOT_WAITTIME
+#define ROOT_WAITTIME 20
+#endif
+
+/*
  * Use partition letters if it's a disk class but not a wedge or flash.
  * XXX Check for wedge/flash is kinda gross.
  */
@@ -185,6 +192,7 @@ char *bootspec;
 void
 setroot(device_t bootdv, int bootpartition)
 {
+	time_t waitend;
 
 	/*
 	 * Let bootcode augment "rootspec", ensure that
@@ -241,14 +249,19 @@ setroot(device_t bootdv, int bootpartiti
 	/*
 	 * loop until a root device is specified
 	 */
+	waitend = time_uptime + ROOT_WAITTIME;
 	do {
 		if (boothowto & RB_ASKNAME)
 			setroot_ask(bootdv, bootpartition);
-		else
+		else {
 			setroot_root(bootdv, bootpartition);
-
-		if (root_device == NULL)
-			boothowto |= RB_ASKNAME;
+			if (root_device == NULL) {
+				if (time_uptime < waitend) {
+					kpause("root", false, hz, NULL);
+				} else
+					boothowto |= RB_ASKNAME;
+			}
+		}
 	} while (root_device == NULL);
 }