kernel: bootrc: add bootloop=

sys/man/8/plan9.ini

@@ -712,6 +712,12 @@ Suppress the
 prompt and use
 .I value
 as the answer instead.
+.SS \fLbootloop=\fIvalue\fP
+Always use
+.I value
+as the answer to the
+.L bootargs
+prompt, retrying if unsuccessful.
 .SS \fLrootdir=\fB/root/\fIdir\fP
 .SS \fLrootspec=\fIspec\fP
 Changes the mount arguments for the root file server

sys/src/9/boot/bootrc

@@ -68,6 +68,11 @@ mt=()
 fn main{
 	mp=()
 	while(~ $#mp 0){
+		if(! ~ $#bootloop 0){
+			nobootprompt=$bootloop
+			# 'flatten' for the next boot
+			echo -n $bootloop > '#ec/bootloop'
+		}
 		if(~ $#nobootprompt 0){
 			echo
 			showlocaldevs

sys/src/9/boot/reboot.rc

@@ -32,6 +32,7 @@ fn connectreboot {
 
 		# set new kernel parameters
 		echo -n $bootargs > '#ec/bootargs'
+		rm -f '#ec/bootloop'
 
 		# remove part of our temporary root
 		/mnt/broot/$cputype/bin/unmount /$cputype/bin /bin