When an attempt to install a line discipline fails, check for

known KLD's that might support it, and load the KLD if found.
Currently the list includes SLIPDISC, PPPDISC, and NETGRAPHDISC.

1 files changed, 57 insertions, 0 deletions

diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index b8eff2c..0d124a2 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -91,6 +91,7 @@
 #include <sys/resourcevar.h>
 #include <sys/malloc.h>
 #include <sys/filedesc.h>
+#include <sys/linker.h>
 #if NSNP > 0
 #include <sys/snoop.h>
 #endif
@@ -113,6 +114,7 @@ static void	ttyrub __P((int c, struct tty *tp));
 static void	ttyrubo __P((struct tty *tp, int cnt));
 static void	ttyunblock __P((struct tty *tp));
 static int	ttywflush __P((struct tty *tp));
+static int	tty_load_disc __P((int t));
 
 /*
  * Table with character classes and parity. The 8th bit indicates parity,
@@ -201,6 +203,23 @@ static u_char const char_type[] = {
 static SLIST_HEAD(, tty) tty_list;
 
 /*
+ * Some line disciplines may exist as external KLD modules.
+ * Put them here and they will be automatically loaded
+ * whenever someone attempts to install the corresponding
+ * line discipline.
+ */
+static struct tty_kldinfo {
+	int		discnum;	/* line discipline number, -1 ends */
+	const char	*filename;	/* name of the KLD file */
+	int		loaded;		/* set to 1 if already loaded */
+} tty_ldisc_klds[] = {
+	{ SLIPDISC,	"if_sl.ko"	},
+	{ PPPDISC,	"if_ppp.ko"	},
+	{ NETGRAPHDISC,	"ng_tty.ko"	},
+	{ -1				}
+};
+
+/*
  * Initial open of tty, or (re)entry to standard tty line discipline.
  */
 int
@@ -960,6 +979,8 @@ ttioctl(tp, cmd, data, flag)
 			s = spltty();
 			(*linesw[tp->t_line].l_close)(tp, flag);
 			error = (*linesw[t].l_open)(device, tp);
+			if (error == ENODEV && tty_load_disc(t)) /* try KLD */
+				error = (*linesw[t].l_open)(device, tp);
 			if (error) {
 				(void)(*linesw[tp->t_line].l_open)(device, tp);
 				splx(s);
@@ -1225,6 +1246,42 @@ again:
 }
 
 /*
+ * Try to load the KLD for the line discipline, if one exists.
+ * Returns 1 on success, zero on failure.
+ */
+static int
+tty_load_disc(int t)
+{
+	struct tty_kldinfo *kld;
+	linker_file_t lf;
+	int error;
+	char *path;
+
+	for (kld = &tty_ldisc_klds[0]; kld->discnum != -1; kld++) {
+		if (kld->discnum == t) {
+
+			/* Don't load the same KLD twice */
+			if (kld->loaded)
+				break;
+
+			/* Try loading the KLD */
+			if ((path = linker_search_path(kld->filename)) == NULL)
+				return 0;
+			error = linker_load_file(path, &lf);
+			FREE(path, M_LINKER);
+			if (error != 0)
+				return 0;
+			lf->userrefs++;		/* as if by kldload(2) */
+
+			/* Mark KLD as loaded and return success */
+			kld->loaded = 1;
+			return 1;
+		}
+	}
+	return 0;
+}
+
+/*
  * Copy in the default termios characters.
  */
 void