Introduce a hooks layer for the MPSAFE TTY layer.

One of the features that prevented us from fixing some of the TTY
consumers to work once again, was an interface that allowed consumers to
do the following:

- `Sniff' incoming data, which is used by the snp(4) driver.

- Take direct control of the input and output paths of a TTY, which is
  used by ng_tty(4), ppp(4), sl(4), etc.

There's no practical advantage in committing a hooks layer without
having any consumers. In P4 there is a preliminary port of snp(4) and
thompsa@ is busy porting ng_tty(4) to this interface. I already want to
have it in the tree, because this may stimulate others to work on the
remaining modules.

Discussed with:	thompsa
Obtained from:	//depot/projects/mpsafetty/...

8 files changed, 341 insertions, 48 deletions

diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index cd6a246..863b6ce 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -36,6 +36,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/conf.h>
 #include <sys/cons.h>
 #include <sys/fcntl.h>
+#include <sys/file.h>
 #include <sys/filio.h>
 #ifdef COMPAT_43TTY
 #include <sys/ioctl_compat.h>
@@ -59,6 +60,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/ttydefaults.h>
 #undef TTYDEFCHARS
 #include <sys/ucred.h>
+#include <sys/vnode.h>
 
 #include <machine/stdarg.h>
 
@@ -855,7 +857,7 @@ tty_alloc(struct ttydevsw *tsw, void *sc, struct mtx *mutex)
 
 	tp = malloc(sizeof(struct tty), M_TTY, M_WAITOK|M_ZERO);
 	tp->t_devsw = tsw;
-	tp->t_softc = sc;
+	tp->t_devswsoftc = sc;
 	tp->t_flags = tsw->tsw_flags;
 
 	tty_init_termios(tp);
@@ -923,7 +925,7 @@ tty_rel_free(struct tty *tp)
 	tty_lock_assert(tp, MA_OWNED);
 
 	if (tp->t_sessioncnt != 0 ||
-	    (tp->t_flags & (TF_GONE|TF_OPENED)) != TF_GONE) {
+	    (tp->t_flags & (TF_GONE|TF_OPENED|TF_HOOK)) != TF_GONE) {
 		/* TTY is still in use. */
 		tty_unlock(tp);
 		return;
@@ -1653,6 +1655,89 @@ tty_hiwat_in_unblock(struct tty *tp)
 		ttydevsw_inwakeup(tp);
 }
 
+static int
+ttyhook_defrint(struct tty *tp, char c, int flags)
+{
+
+	if (ttyhook_rint_bypass(tp, &c, 1) != 1)
+		return (-1);
+	
+	return (0);
+}
+
+int
+ttyhook_register(struct tty **rtp, struct thread *td, int fd,
+    struct ttyhook *th, void *softc)
+{
+	struct tty *tp;
+	struct file *fp;
+	struct cdev *dev;
+	struct cdevsw *cdp;
+	int error;
+
+	/* Validate the file descriptor. */
+	if (fget(td, fd, &fp) != 0)
+		return (EINVAL);
+	
+	/* Make sure the vnode is bound to a character device. */
+	error = EINVAL;
+	if (fp->f_type != DTYPE_VNODE || fp->f_vnode->v_type != VCHR ||
+	    fp->f_vnode->v_rdev == NULL)
+		goto done1;
+	dev = fp->f_vnode->v_rdev;
+
+	/* Make sure it is a TTY. */
+	cdp = dev_refthread(dev);
+	if (cdp == NULL)
+		goto done1;
+	if ((cdp->d_flags & D_TTY) == 0)
+		goto done2;
+	tp = dev->si_drv1;
+
+	/* Try to attach the hook to the TTY. */
+	error = EBUSY;
+	tty_lock(tp);
+	MPASS((tp->t_hook == NULL) == ((tp->t_flags & TF_HOOK) == 0));
+	if (tp->t_flags & TF_HOOK)
+		goto done3;
+
+	tp->t_flags |= TF_HOOK;
+	tp->t_hook = th;
+	tp->t_hooksoftc = softc;
+	*rtp = tp;
+	error = 0;
+
+	/* Maybe we can switch into bypass mode now. */
+	ttydisc_optimize(tp);
+
+	/* Silently convert rint() calls to rint_bypass() when possible. */
+	if (!ttyhook_hashook(tp, rint) && ttyhook_hashook(tp, rint_bypass))
+		th->th_rint = ttyhook_defrint;
+
+done3:	tty_unlock(tp);
+done2:	dev_relthread(dev);
+done1:	fdrop(fp, td);
+	return (error);
+}
+
+void
+ttyhook_unregister(struct tty *tp)
+{
+
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(tp->t_flags & TF_HOOK);
+
+	/* Disconnect the hook. */
+	tp->t_flags &= ~TF_HOOK;
+	tp->t_hook = NULL;
+
+	/* Maybe we need to leave bypass mode. */
+	ttydisc_optimize(tp);
+
+	/* Maybe deallocate the TTY as well. */
+	tty_rel_free(tp);
+}
+
 #include "opt_ddb.h"
 #ifdef DDB
 #include <ddb/ddb.h>
@@ -1686,6 +1771,7 @@ static struct {
 	{ TF_EXCLUDE,	'X' },
 	{ TF_BYPASS,	'l' },
 	{ TF_ZOMBIE,	'Z' },
+	{ TF_HOOK,	's' },
 
 	{ 0,	       '\0' },
 };
diff --git a/sys/kern/tty_ttydisc.c b/sys/kern/tty_ttydisc.c
index 693b480..0d7dd7f 100644
--- a/sys/kern/tty_ttydisc.c
+++ b/sys/kern/tty_ttydisc.c
@@ -79,6 +79,8 @@ SYSCTL_LONG(_kern, OID_AUTO, tty_nout, CTLFLAG_RD,
 #define CTL_ALNUM(c)	(((c) >= '0' && (c) <= '9') || \
     ((c) >= 'a' && (c) <= 'z') || ((c) >= 'A' && (c) <= 'Z'))
 
+#define	TTY_STACKBUF	256
+
 void
 ttydisc_open(struct tty *tp)
 {
@@ -100,6 +102,9 @@ ttydisc_close(struct tty *tp)
 		ttydevsw_inwakeup(tp);
 		ttydevsw_outwakeup(tp);
 	}
+
+	if (ttyhook_hashook(tp, close))
+		ttyhook_close(tp);
 }
 
 static int
@@ -433,7 +438,7 @@ ttydisc_write_oproc(struct tty *tp, char c)
 int
 ttydisc_write(struct tty *tp, struct uio *uio, int ioflag)
 {
-	char ob[256];
+	char ob[TTY_STACKBUF];
 	char *obstart;
 	int error = 0;
 	unsigned int oblen = 0;
@@ -557,11 +562,12 @@ ttydisc_optimize(struct tty *tp)
 {
 	tty_lock_assert(tp, MA_OWNED);
 
-	if (!CMP_FLAG(i, ICRNL|IGNCR|IMAXBEL|INLCR|ISTRIP|IXON) &&
+	if ((!CMP_FLAG(i, ICRNL|IGNCR|IMAXBEL|INLCR|ISTRIP|IXON) &&
 	    (!CMP_FLAG(i, BRKINT) || CMP_FLAG(i, IGNBRK)) &&
 	    (!CMP_FLAG(i, PARMRK) ||
 	        CMP_FLAG(i, IGNPAR|IGNBRK) == (IGNPAR|IGNBRK)) &&
-	    !CMP_FLAG(l, ECHO|ICANON|IEXTEN|ISIG|PENDIN)) {
+	    !CMP_FLAG(l, ECHO|ICANON|IEXTEN|ISIG|PENDIN)) ||
+	    ttyhook_hashook(tp, rint_bypass)) {
 		tp->t_flags |= TF_BYPASS;
 	} else {
 		tp->t_flags &= ~TF_BYPASS;
@@ -818,6 +824,9 @@ ttydisc_rint(struct tty *tp, char c, int flags)
 	tty_lock_assert(tp, MA_OWNED);
 
 	atomic_add_long(&tty_nin, 1);
+
+	if (ttyhook_hashook(tp, rint))
+		return ttyhook_rint(tp, c, flags);
 	
 	if (tp->t_flags & TF_BYPASS)
 		goto processed;
@@ -1045,6 +1054,9 @@ ttydisc_rint_bypass(struct tty *tp, const void *buf, size_t len)
 
 	atomic_add_long(&tty_nin, len);
 
+	if (ttyhook_hashook(tp, rint_bypass))
+		return ttyhook_rint_bypass(tp, buf, len);
+
 	ret = ttyinq_write(&tp->t_inq, buf, len, 0);
 	ttyinq_canonicalize(&tp->t_inq);
 
@@ -1057,12 +1069,38 @@ ttydisc_rint_done(struct tty *tp)
 
 	tty_lock_assert(tp, MA_OWNED);
 
+	if (ttyhook_hashook(tp, rint_done))
+		ttyhook_rint_done(tp);
+
 	/* Wake up readers. */
 	tty_wakeup(tp, FREAD);
 	/* Wake up driver for echo. */
 	ttydevsw_outwakeup(tp);
 }
 
+size_t
+ttydisc_rint_poll(struct tty *tp)
+{
+	size_t l;
+
+	tty_lock_assert(tp, MA_OWNED);
+
+	if (ttyhook_hashook(tp, rint_poll))
+		return ttyhook_rint_poll(tp);
+
+	/*
+	 * XXX: Still allow character input when there's no space in the
+	 * buffers, but we haven't entered the high watermark. This is
+	 * to allow backspace characters to be inserted when in
+	 * canonical mode.
+	 */
+	l = ttyinq_bytesleft(&tp->t_inq);
+	if (l == 0 && (tp->t_flags & TF_HIWAT_IN) == 0)
+		return (1);
+	
+	return (l);
+}
+
 static void
 ttydisc_wakeup_watermark(struct tty *tp)
 {
@@ -1093,9 +1131,15 @@ ttydisc_getc(struct tty *tp, void *buf, size_t len)
 	if (tp->t_flags & TF_STOPPED)
 		return (0);
 
+	if (ttyhook_hashook(tp, getc_inject))
+		return ttyhook_getc_inject(tp, buf, len);
+
 	len = ttyoutq_read(&tp->t_outq, buf, len);
-	ttydisc_wakeup_watermark(tp);
 
+	if (ttyhook_hashook(tp, getc_capture))
+		ttyhook_getc_capture(tp, buf, len);
+
+	ttydisc_wakeup_watermark(tp);
 	atomic_add_long(&tty_nout, len);
 
 	return (len);
@@ -1104,22 +1148,63 @@ ttydisc_getc(struct tty *tp, void *buf, size_t len)
 int
 ttydisc_getc_uio(struct tty *tp, struct uio *uio)
 {
-	int error;
+	int error = 0;
 	int obytes = uio->uio_resid;
+	size_t len;
+	char buf[TTY_STACKBUF];
 
 	tty_lock_assert(tp, MA_OWNED);
 
 	if (tp->t_flags & TF_STOPPED)
 		return (0);
 
-	error = ttyoutq_read_uio(&tp->t_outq, tp, uio);
-	ttydisc_wakeup_watermark(tp);
+	/*
+	 * When a TTY hook is attached, we cannot perform unbuffered
+	 * copying to userspace. Just call ttydisc_getc() and
+	 * temporarily store data in a shadow buffer.
+	 */
+	if (ttyhook_hashook(tp, getc_capture) ||
+	    ttyhook_hashook(tp, getc_inject)) {
+		while (uio->uio_resid > 0) {
+			/* Read to shadow buffer. */
+			len = ttydisc_getc(tp, buf,
+			    MIN(uio->uio_resid, sizeof buf));
+			if (len == 0)
+				break;
+
+			/* Copy to userspace. */
+			tty_unlock(tp);
+			error = uiomove(buf, len, uio);
+			tty_lock(tp);
+			
+			if (error != 0)
+				break;
+		}
+	} else {
+		error = ttyoutq_read_uio(&tp->t_outq, tp, uio);
 
-	atomic_add_long(&tty_nout, obytes - uio->uio_resid);
+		ttydisc_wakeup_watermark(tp);
+		atomic_add_long(&tty_nout, obytes - uio->uio_resid);
+	}
 
 	return (error);
 }
 
+size_t
+ttydisc_getc_poll(struct tty *tp)
+{
+
+	tty_lock_assert(tp, MA_OWNED);
+
+	if (tp->t_flags & TF_STOPPED)
+		return (0);
+
+	if (ttyhook_hashook(tp, getc_poll))
+		return ttyhook_getc_poll(tp);
+
+	return ttyoutq_bytesused(&tp->t_outq);
+}
+
 /*
  * XXX: not really related to the TTYDISC, but we'd better put
  * tty_putchar() here, because we need to perform proper output
diff --git a/sys/sys/tty.h b/sys/sys/tty.h
index 54d487c..2250cbc 100644
--- a/sys/sys/tty.h
+++ b/sys/sys/tty.h
@@ -80,6 +80,7 @@ struct tty {
 #define	TF_EXCLUDE	0x1000	/* Exclusive access. */
 #define	TF_BYPASS	0x2000	/* Optimized input path. */
 #define	TF_ZOMBIE	0x4000	/* Modem disconnect received. */
+#define	TF_HOOK		0x8000	/* TTY has hook attached. */
 	unsigned int	t_revokecnt;	/* (t) revoke() count. */
 
 	/* Buffering mechanisms. */
@@ -112,13 +113,15 @@ struct tty {
 	struct termios	t_termios_lock_out;	/* cua%s.lock. */
 
 	struct ttydevsw	*t_devsw;	/* (c) Driver hooks. */
+	struct ttyhook	*t_hook;	/* (t) Capture/inject hook. */
 
 	/* Process signal delivery. */
 	struct pgrp	*t_pgrp;	/* (t) Foreground process group. */
 	struct session	*t_session;	/* (t) Associated session. */
 	unsigned int	t_sessioncnt;	/* (t) Backpointing sessions. */
 
-	void		*t_softc;	/* (c) Soft config, for drivers. */
+	void		*t_devswsoftc;	/* (c) Soft config, for drivers. */
+	void		*t_hooksoftc;	/* (t) Soft config, for hooks. */
 	struct cdev	*t_dev;		/* (c) Primary character device. */
 };
 
@@ -181,7 +184,7 @@ void	tty_hiwat_in_unblock(struct tty *tp);
 dev_t	tty_udev(struct tty *tp);
 #define	tty_opened(tp)		((tp)->t_flags & TF_OPENED)
 #define	tty_gone(tp)		((tp)->t_flags & TF_GONE)
-#define	tty_softc(tp)		((tp)->t_softc)
+#define	tty_softc(tp)		((tp)->t_devswsoftc)
 #define	tty_devname(tp)		devtoname((tp)->t_dev)
 
 /* Status line printing. */
@@ -192,8 +195,9 @@ int	pts_alloc_external(int fd, struct thread *td, struct file *fp,
     struct cdev *dev, const char *name);
 
 /* Drivers and line disciplines also need to call these. */
-#include <sys/ttydevsw.h>
 #include <sys/ttydisc.h>
+#include <sys/ttydevsw.h>
+#include <sys/ttyhook.h>
 #endif /* _KERNEL */
 
 #endif /* !_SYS_TTY_H_ */
diff --git a/sys/sys/ttydevsw.h b/sys/sys/ttydevsw.h
index 842143d..e2278c3 100644
--- a/sys/sys/ttydevsw.h
+++ b/sys/sys/ttydevsw.h
@@ -97,9 +97,7 @@ ttydevsw_outwakeup(struct tty *tp)
 	MPASS(!tty_gone(tp));
 
 	/* Prevent spurious wakeups. */
-	if (tp->t_flags & TF_STOPPED)
-		return;
-	if (ttyoutq_bytesused(&tp->t_outq) == 0)
+	if (ttydisc_getc_poll(tp) == 0)
 		return;
 
 	tp->t_devsw->tsw_outwakeup(tp);
diff --git a/sys/sys/ttydisc.h b/sys/sys/ttydisc.h
index aeaabc6..2ea5466 100644
--- a/sys/sys/ttydisc.h
+++ b/sys/sys/ttydisc.h
@@ -54,8 +54,10 @@ void	ttydisc_modem(struct tty *tp, int open);
 int	ttydisc_rint(struct tty *tp, char c, int flags);
 size_t	ttydisc_rint_bypass(struct tty *tp, const void *buf, size_t len);
 void	ttydisc_rint_done(struct tty *tp);
+size_t	ttydisc_rint_poll(struct tty *tp);
 size_t	ttydisc_getc(struct tty *tp, void *buf, size_t len);
 int	ttydisc_getc_uio(struct tty *tp, struct uio *uio);
+size_t	ttydisc_getc_poll(struct tty *tp);
 
 /* Error codes for ttydisc_rint(). */
 #define	TRE_FRAMING	0x01
@@ -81,36 +83,4 @@ ttydisc_write_poll(struct tty *tp)
 	return ttyoutq_bytesleft(&tp->t_outq);
 }
 
-static __inline size_t
-ttydisc_rint_poll(struct tty *tp)
-{
-	size_t l;
-
-	tty_lock_assert(tp, MA_OWNED);
-
-	/*
-	 * XXX: Still allow character input when there's no space in the
-	 * buffers, but we haven't entered the high watermark. This is
-	 * to allow backspace characters to be inserted when in
-	 * canonical mode.
-	 */
-	l = ttyinq_bytesleft(&tp->t_inq);
-	if (l == 0 && (tp->t_flags & TF_HIWAT_IN) == 0)
-		return (1);
-	
-	return (l);
-}
-
-static __inline size_t
-ttydisc_getc_poll(struct tty *tp)
-{
-
-	tty_lock_assert(tp, MA_OWNED);
-
-	if (tp->t_flags & TF_STOPPED)
-		return (0);
-
-	return ttyoutq_bytesused(&tp->t_outq);
-}
-
 #endif /* !_SYS_TTYDISC_H_ */
diff --git a/sys/sys/ttyhook.h b/sys/sys/ttyhook.h
new file mode 100644
index 0000000..7a0a0bc
--- /dev/null
+++ b/sys/sys/ttyhook.h
@@ -0,0 +1,147 @@
+/*-
+ * Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef _SYS_TTYHOOK_H_
+#define	_SYS_TTYHOOK_H_
+
+#ifndef _SYS_TTY_H_
+#error "can only be included through <sys/tty.h>"
+#endif /* !_SYS_TTY_H_ */
+
+struct tty;
+
+/*
+ * Hooks interface, which allows to capture and inject traffic into the
+ * input and output paths of a TTY.
+ */
+
+typedef int th_rint_t(struct tty *tp, char c, int flags);
+typedef size_t th_rint_bypass_t(struct tty *tp, const void *buf, size_t len);
+typedef void th_rint_done_t(struct tty *tp);
+typedef size_t th_rint_poll_t(struct tty *tp);
+
+typedef size_t th_getc_inject_t(struct tty *tp, void *buf, size_t len);
+typedef void th_getc_capture_t(struct tty *tp, const void *buf, size_t len);
+typedef size_t th_getc_poll_t(struct tty *tp);
+
+typedef void th_close_t(struct tty *tp);
+
+struct ttyhook {
+	/* Character input. */
+	th_rint_t		*th_rint;
+	th_rint_bypass_t	*th_rint_bypass;
+	th_rint_done_t		*th_rint_done;
+	th_rint_poll_t		*th_rint_poll;
+
+	/* Character output. */
+	th_getc_inject_t	*th_getc_inject;
+	th_getc_capture_t	*th_getc_capture;
+	th_getc_poll_t		*th_getc_poll;
+
+	th_close_t		*th_close;
+};
+
+int	ttyhook_register(struct tty **, struct thread *, int,
+    struct ttyhook *, void *);
+void	ttyhook_unregister(struct tty *);
+#define	ttyhook_softc(tp)		((tp)->t_hooksoftc)
+#define	ttyhook_hashook(tp,hook)	((tp)->t_hook != NULL && \
+					(tp)->t_hook->th_ ## hook != NULL)
+
+static __inline int
+ttyhook_rint(struct tty *tp, char c, int flags)
+{
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(!tty_gone(tp));
+
+	return tp->t_hook->th_rint(tp, c, flags);
+}
+
+static __inline size_t
+ttyhook_rint_bypass(struct tty *tp, const void *buf, size_t len)
+{
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(!tty_gone(tp));
+
+	return tp->t_hook->th_rint_bypass(tp, buf, len);
+}
+
+static __inline void
+ttyhook_rint_done(struct tty *tp)
+{
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(!tty_gone(tp));
+
+	tp->t_hook->th_rint_done(tp);
+}
+
+static __inline size_t
+ttyhook_rint_poll(struct tty *tp)
+{
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(!tty_gone(tp));
+
+	return tp->t_hook->th_rint_poll(tp);
+}
+
+static __inline size_t
+ttyhook_getc_inject(struct tty *tp, void *buf, size_t len)
+{
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(!tty_gone(tp));
+
+	return tp->t_hook->th_getc_inject(tp, buf, len);
+}
+
+static __inline void
+ttyhook_getc_capture(struct tty *tp, const void *buf, size_t len)
+{
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(!tty_gone(tp));
+
+	tp->t_hook->th_getc_capture(tp, buf, len);
+}
+
+static __inline size_t
+ttyhook_getc_poll(struct tty *tp)
+{
+	tty_lock_assert(tp, MA_OWNED);
+	MPASS(!tty_gone(tp));
+
+	return tp->t_hook->th_getc_poll(tp);
+}
+
+static __inline void
+ttyhook_close(struct tty *tp)
+{
+	tty_lock_assert(tp, MA_OWNED);
+
+	tp->t_hook->th_close(tp);
+}
+
+#endif /* !_SYS_TTYHOOK_H_ */
diff --git a/usr.sbin/pstat/pstat.8 b/usr.sbin/pstat/pstat.8
index 2770cb7..5474f8b 100644
--- a/usr.sbin/pstat/pstat.8
+++ b/usr.sbin/pstat/pstat.8
@@ -202,6 +202,8 @@ output stopped (ixon flow control)
 block mode input routine in use
 .It Z
 connection lost
+.It s
+i/o being snooped
 .El
 .Pp
 The
diff --git a/usr.sbin/pstat/pstat.c b/usr.sbin/pstat/pstat.c
index 51828cb..a1e81b3 100644
--- a/usr.sbin/pstat/pstat.c
+++ b/usr.sbin/pstat/pstat.c
@@ -312,6 +312,7 @@ static struct {
 	{ TF_EXCLUDE,	'X' },
 	{ TF_BYPASS,	'l' },
 	{ TF_ZOMBIE,	'Z' },
+	{ TF_HOOK,	's' },
 
 	{ 0,	       '\0' },
 };