From ccfd3aab30efce20f676555ea7b1eeb4bd5a8e1d Mon Sep 17 00:00:00 2001
From: Ed Schouten <ed@FreeBSD.org>
Date: Sat, 25 Apr 2009 10:05:55 +0000
Subject: [PATCH] Turn MAXPTSDEVS into a sysctl tunable.

This allows users to increase the maximum amount of pseudo-terminals
without changing any source code. Users must increase UT_LINESIZE before
attempting to increase kern.pts_maxdev.
---
 share/man/man4/pts.4 | 20 ++++++++++++++++++++
 sys/kern/tty_pts.c   | 19 +++++++++++++++++--
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/share/man/man4/pts.4 b/share/man/man4/pts.4
index 9ae2d73beec7..294f1ef02174 100644
--- a/share/man/man4/pts.4
+++ b/share/man/man4/pts.4
@@ -156,6 +156,26 @@ though
 .It Pa /dev/pts/[num]
 Pseudo-terminal slave devices.
 .El
+.Sh SYSCTL VARIABLES
+The following
+.Xr sysctl 8
+variables can be used to modify or monitor
+.Nm
+behavior.
+.Bl -tag -width indent
+.It Va kern.pts_maxdev
+Highest pseudo-terminal unit number to be allocated.
+Because
+.Xr utmp 5
+is restricted to an 8-byte line name size,
+.Nm
+will not create any pseudo-terminals with a unit number above 999 by
+default.
+After increasing
+.Dv UT_LINESIZE ,
+this variable can be changed to allow more than 1000 pseudo-terminals to
+be allocated simultaneously.
+.El
 .Sh DIAGNOSTICS
 None.
 .Sh SEE ALSO
diff --git a/sys/kern/tty_pts.c b/sys/kern/tty_pts.c
index 74ab18577763..67704b8eaa9f 100644
--- a/sys/kern/tty_pts.c
+++ b/sys/kern/tty_pts.c
@@ -50,6 +50,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/filedesc.h>
 #include <sys/filio.h>
 #include <sys/kernel.h>
+#include <sys/limits.h>
 #include <sys/malloc.h>
 #include <sys/poll.h>
 #include <sys/proc.h>
@@ -58,6 +59,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/stat.h>
 #include <sys/syscall.h>
 #include <sys/syscallsubr.h>
+#include <sys/sysctl.h>
 #include <sys/sysent.h>
 #include <sys/sysproto.h>
 #include <sys/systm.h>
@@ -66,8 +68,16 @@ __FBSDID("$FreeBSD$");
 
 #include <machine/stdarg.h>
 
+/*
+ * Our utmp(5) format is limited to 8-byte TTY line names.  This means
+ * we can at most allocate 1000 pseudo-terminals ("pts/999").  Allow
+ * users to increase this number, assuming they have manually increased
+ * UT_LINESIZE.
+ */
 static struct unrhdr *pts_pool;
-#define MAXPTSDEVS 999
+static unsigned int pts_maxdev = 999;
+SYSCTL_UINT(_kern, OID_AUTO, pts_maxdev, CTLFLAG_RW, &pts_maxdev, 0,
+    "Maximum amount of pts(4) pseudo-terminals");
 
 static MALLOC_DEFINE(M_PTS, "pts", "pseudo tty device");
 
@@ -716,6 +726,11 @@ pts_alloc(int fflags, struct thread *td, struct file *fp)
 		chgptscnt(uid, -1, 0);
 		return (EAGAIN);
 	}
+	if (unit > pts_maxdev) {
+		free_unr(pts_pool, unit);
+		chgptscnt(uid, -1, 0);
+		return (EAGAIN);
+	}
 
 	/* Allocate TTY and softc. */
 	psc = malloc(sizeof(struct pts_softc), M_PTS, M_WAITOK|M_ZERO);
@@ -829,7 +844,7 @@ static void
 pts_init(void *unused)
 {
 
-	pts_pool = new_unrhdr(0, MAXPTSDEVS, NULL);
+	pts_pool = new_unrhdr(0, INT_MAX, NULL);
 #if defined(PTS_COMPAT) || defined(PTS_LINUX)
 	make_dev(&ptmx_cdevsw, 0, UID_ROOT, GID_WHEEL, 0666, "ptmx");
 #endif /* PTS_COMPAT || PTS_LINUX */