Add a -k option to reboot to specify the kernel to boot next time

around.  If the kernel boots successfully, the record of this kernel
is erased, it is intended to be a one-shot option for testing
kernels.

This could be improved by having the loader remove the record of
the next kernel to boot, it is currently removed in /etc/rc immediately
after disks are mounted r/w.

I'd like to MFC this before the 4.6 freeze unless there is violent
objection.

Reviewed by:	Several on IRC
MFC after:	4 days

2 files changed, 34 insertions, 5 deletions

diff --git a/sbin/reboot/reboot.8 b/sbin/reboot/reboot.8
index a16eef1..bf914b1 100644
--- a/sbin/reboot/reboot.8
+++ b/sbin/reboot/reboot.8
@@ -44,12 +44,16 @@
 .Sh SYNOPSIS
 .Nm halt
 .Op Fl lnqp
+.Op Fl k Ar kernel
 .Nm
 .Op Fl dlnqp
+.Op Fl k Ar kernel
 .Nm fasthalt
 .Op Fl lnqp
+.Op Fl k Ar kernel
 .Nm fastboot
 .Op Fl dlnqp
+.Op Fl k Ar kernel
 .Sh DESCRIPTION
 The
 .Nm halt
@@ -72,6 +76,16 @@ The system is requested to create a crash dump.  This option is
 supported only when rebooting, and it has no effect unless a dump
 device has previously been specified with
 .Xr dumpon 8 .
+.It Fl k Ar kernel
+Boot the specified
+.Ar kernel
+on the next system boot.  If the kernel boots successfully, the 
+.Em default
+kernel will be booted on succesive boots, this is a one-shot option.
+If the boot fails, the system will continue attempting to boot
+.Ar kernel
+until the boot process is interrupted and a valid kernel booted.
+This may change in the future.
 .It Fl l
 The halt or reboot is
 .Em not
diff --git a/sbin/reboot/reboot.c b/sbin/reboot/reboot.c
index 61f971d..be8911f 100644
--- a/sbin/reboot/reboot.c
+++ b/sbin/reboot/reboot.c
@@ -51,6 +51,7 @@ static const char rcsid[] =
 #include <signal.h>
 #include <err.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <libutil.h>
 #include <pwd.h>
 #include <syslog.h>
@@ -68,9 +69,9 @@ int
 main(int argc, char *argv[])
 {
 	struct passwd *pw;
-	int ch, howto, i, lflag, nflag, qflag, pflag, sverrno;
+	int ch, howto, i, fd, kflag, lflag, nflag, qflag, pflag, sverrno;
 	u_int pageins;
-	char *p;
+	char *kernel, *p;
 	const char *user;
 
 	if (strstr((p = rindex(*argv, '/')) ? p + 1 : *argv, "halt")) {
@@ -78,12 +79,16 @@ main(int argc, char *argv[])
 		howto = RB_HALT;
 	} else
 		howto = 0;
-	lflag = nflag = qflag = 0;
-	while ((ch = getopt(argc, argv, "dlnpq")) != -1)
+	kflag = lflag = nflag = qflag = 0;
+	while ((ch = getopt(argc, argv, "dk:lnpq")) != -1)
 		switch(ch) {
 		case 'd':
 			howto |= RB_DUMP;
 			break;
+		case 'k':
+			kflag = 1;
+			kernel = optarg;
+			break;
 		case 'l':
 			lflag = 1;
 			break;
@@ -117,6 +122,16 @@ main(int argc, char *argv[])
 		err(1, NULL);
 	}
 
+	if (kflag) {
+		fd = open("/boot/nextkernel", O_WRONLY | O_CREAT, 0444);
+		if (fd > -1) {
+			(void)write(fd, "kernel=\"", 8L);
+			(void)write(fd, kernel, strlen(kernel));
+			(void)write(fd, "\"\n", 2);
+			close(fd);
+		}
+	}
+
 	/* Log the reboot. */
 	if (!lflag)  {
 		if ((user = getlogin()) == NULL)
@@ -195,7 +210,7 @@ restart:
 void
 usage()
 {
-	(void)fprintf(stderr, "usage: %s [-dnpq]\n",
+	(void)fprintf(stderr, "usage: %s [-dnpq] [-k kernel]\n",
 	    dohalt ? "halt" : "reboot");
 	exit(1);
 }