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From:   Walt Drummond <walt@drummond.us>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>
Cc:     ar@cs.msu.ru, linux-kernel@vger.kernel.org, walt@drummond.us
Subject: [PATCH 3/3] status: Display an informational message when the VSTATUS character is pressed or TIOCSTAT ioctl is called.
Date:   Mon, 17 Jan 2022 20:43:23 -0800
Message-Id: <20220118044323.765038-3-walt@drummond.us>
In-Reply-To: <20220118044323.765038-1-walt@drummond.us>
References: <20220118044323.765038-1-walt@drummond.us>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When triggered by pressing the VSTATUS key or calling the TIOCSTAT
ioctl, the n_tty line discipline will display a message on the user's
tty that provides basic information about the system and an
'interesting' process in the current foreground process group, eg:

  load: 0.58  cmd: sleep 744474 [sleeping] 0.36r 0.00u 0.00s 0% 772k

The status message provides:
 - System load average
 - Command name and process id (from the perspective of the session)
 - Scheduler state
 - Total wall-clock run time
 - User space run time
 - System space run time
 - Percentage of on-cpu time
 - Resident set size

The message is only displayed when the tty has the VSTATUS character
set and the local flag NOKERNINFO disabled; it is always displayed
when TIOCSTAT is called regardless of tty settings.

Signed-off-by: Walt Drummond <walt@drummond.us>
---
 drivers/tty/Makefile       |   2 +-
 drivers/tty/n_tty.c        |  37 +++++++++
 drivers/tty/n_tty_status.c | 162 +++++++++++++++++++++++++++++++++++++
 drivers/tty/tty_io.c       |   2 +-
 include/linux/tty.h        | 123 ++++++++++++++--------------
 5 files changed, 265 insertions(+), 61 deletions(-)
 create mode 100644 drivers/tty/n_tty_status.c

diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index 07aca5184a55..84bc99aebcff 100644
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -2,7 +2,7 @@
 obj-$(CONFIG_TTY)		+= tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \
 				   tty_buffer.o tty_port.o tty_mutex.o \
 				   tty_ldsem.o tty_baudrate.o tty_jobctrl.o \
-				   n_null.o
+				   n_null.o n_tty_status.o
 obj-$(CONFIG_LEGACY_PTYS)	+= pty.o
 obj-$(CONFIG_UNIX98_PTYS)	+= pty.o
 obj-$(CONFIG_AUDIT)		+= tty_audit.o
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 6a6e7da80095..2e9b038e84e0 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -80,6 +80,7 @@
 #define ECHO_BLOCK		256
 #define ECHO_DISCARD_WATERMARK	N_TTY_BUF_SIZE - (ECHO_BLOCK + 32)
 
+#define STATUS_LINE_LEN 160	/* tty status line will truncate at this length */
 
 #undef N_TTY_TRACE
 #ifdef N_TTY_TRACE
@@ -127,6 +128,8 @@ struct n_tty_data {
 	struct mutex output_lock;
 };
 
+static int n_tty_status(struct tty_struct *tty);
+
 #define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1))
 
 static inline size_t read_cnt(struct n_tty_data *ldata)
@@ -1334,6 +1337,11 @@ static void n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
 			commit_echoes(tty);
 			return;
 		}
+		if (c == STATUS_CHAR(tty)) {
+			if (!L_NOKERNINFO(tty))
+				n_tty_status(tty);
+			return;
+		}
 		if (c == '\n') {
 			if (L_ECHO(tty) || L_ECHONL(tty)) {
 				echo_char_raw('\n', ldata);
@@ -1763,6 +1771,7 @@ static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
 			set_bit(EOF_CHAR(tty), ldata->char_map);
 			set_bit('\n', ldata->char_map);
 			set_bit(EOL_CHAR(tty), ldata->char_map);
+			set_bit(STATUS_CHAR(tty), ldata->char_map);
 			if (L_IEXTEN(tty)) {
 				set_bit(WERASE_CHAR(tty), ldata->char_map);
 				set_bit(LNEXT_CHAR(tty), ldata->char_map);
@@ -2412,6 +2421,29 @@ static unsigned long inq_canon(struct n_tty_data *ldata)
 	return nr;
 }
 
+static int n_tty_status(struct tty_struct *tty)
+{
+	struct n_tty_data *ldata = tty->disc_data;
+	char *buf, msg[STATUS_LINE_LEN] = {0};
+	int ret = 0;
+	size_t len = STATUS_LINE_LEN - 1;
+
+	buf = (char *) &msg;
+	ret = n_tty_get_status(tty, buf + 1, &len);
+	if (ret)
+		return ret;
+
+	if (ldata->column != 0) {
+		msg[0] = '\n';
+		len++;
+	} else {
+		buf++;
+	}
+
+	do_n_tty_write(tty, NULL, buf, len);
+	return 0;
+}
+
 static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
 		       unsigned int cmd, unsigned long arg)
 {
@@ -2429,6 +2461,11 @@ static int n_tty_ioctl(struct tty_struct *tty, struct file *file,
 			retval = read_cnt(ldata);
 		up_write(&tty->termios_rwsem);
 		return put_user(retval, (unsigned int __user *) arg);
+	case TIOCSTAT:
+		down_read(&tty->termios_rwsem);
+		retval = n_tty_status(tty);
+		up_read(&tty->termios_rwsem);
+		return retval;
 	default:
 		return n_tty_ioctl_helper(tty, cmd, arg);
 	}
diff --git a/drivers/tty/n_tty_status.c b/drivers/tty/n_tty_status.c
new file mode 100644
index 000000000000..269776db0640
--- /dev/null
+++ b/drivers/tty/n_tty_status.c
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-1.0+
+/*
+ * n_tty_status.c --- implements VSTATUS and TIOCSTAT from BSD
+ *
+ * Display a basic status message containing information about the
+ * foreground process and system load on the users tty, triggered by
+ * the VSTATUS character or TIOCSTAT. Ex,
+ *
+ *   load: 14.11  cmd: tcsh 19623 [running] 185756.62r 88.00u 17.50s 0% 4260k
+ *
+ */
+
+#include <linux/tty.h>
+#include <linux/mm.h>
+#include <linux/sched/loadavg.h>
+
+static const char * const task_state_unknown = "unknown";
+static const char * const task_state_array[] = {
+	"running",
+	"sleeping",
+	"disk sleep",
+	"stopped",
+	"tracing stop",
+	"dead",
+	"zombie",
+	"parked",
+	"idle",
+};
+
+static inline unsigned long getRSSk(struct mm_struct *mm)
+{
+	if (mm == NULL)
+		return 0;
+	return get_mm_rss(mm) * PAGE_SIZE / 1024;
+}
+
+static inline long frac_sec(long l)
+{
+	l /= NSEC_PER_MSEC * 10;
+	if (l < 10)
+		l *= 10;
+	return l;
+}
+
+static inline struct task_struct *compare(struct task_struct *new,
+					  struct task_struct *old)
+{
+	unsigned int ostate, nstate;
+
+	if (old == NULL)
+		return new;
+
+	ostate = task_state_index(old);
+	nstate = task_state_index(new);
+
+	if (ostate == nstate) {
+		if (old->start_time > new->start_time)
+			return old;
+		return new;
+	}
+
+	if (ostate < nstate)
+		return old;
+
+	return new;
+}
+
+static struct task_struct *pick_process(struct pid *pgrp)
+{
+	struct task_struct *new, *winner = NULL;
+
+	read_lock(&tasklist_lock);
+	do_each_pid_task(pgrp, PIDTYPE_PGID, new) {
+		winner = compare(new, winner);
+	} while_each_pid_task(pgrp, PIDTYPE_PGID, new);
+	read_unlock(&tasklist_lock);
+
+	return winner;
+}
+
+/* We want the pid from the context of session */
+static inline pid_t __get_pid(struct task_struct *tsk, struct tty_struct *tty)
+{
+	return __task_pid_nr_ns(tsk, PIDTYPE_PID, ns_of_pid(tty->ctrl.session));
+}
+
+static inline const char *get_task_state_name(struct task_struct *tsk)
+{
+
+	int index;
+
+	index = task_state_index(tsk);
+	if (index > ARRAY_SIZE(task_state_array))
+		return task_state_unknown;
+	return task_state_array[index];
+}
+
+int n_tty_get_status(struct tty_struct *tty, char *msg, size_t *msglen)
+{
+	unsigned long loadavg[3];
+	uint64_t pcpu, cputime, wallclock;
+	struct task_struct *p;
+	struct rusage rusage;
+	struct timespec64 utime, stime, rtime;
+	char tname[TASK_COMM_LEN];
+	size_t len;
+
+	if (tty == NULL)
+		return -ENOTTY;
+
+	get_avenrun(loadavg, FIXED_1/200, 0);
+	len = scnprintf(msg + len, *msglen - len, "load: %lu.%02lu  ",
+			LOAD_INT(loadavg[0]), LOAD_FRAC(loadavg[0]));
+
+	if (tty->ctrl.session == NULL) {
+		len += scnprintf(msg + len, *msglen - len,
+				 "not a controlling terminal\n");
+		goto out;
+	}
+
+	if (tty->ctrl.pgrp == NULL) {
+		len += scnprintf(msg + len, *msglen - len,
+				 "no foreground process group\n");
+		goto out;
+	}
+
+	p = pick_process(tty->ctrl.pgrp);
+	if (p == NULL) {
+		len += scnprintf(msg + len, *msglen - len,
+				 "empty foreground process group\n");
+		goto out;
+	}
+
+	get_task_comm(tname, p);
+	getrusage(p, RUSAGE_BOTH, &rusage);
+	wallclock = ktime_get_ns() - p->start_time;
+
+	utime.tv_sec = rusage.ru_utime.tv_sec;
+	utime.tv_nsec = rusage.ru_utime.tv_usec * NSEC_PER_USEC;
+	stime.tv_sec = rusage.ru_stime.tv_sec;
+	stime.tv_nsec = rusage.ru_stime.tv_usec * NSEC_PER_USEC;
+	rtime = ns_to_timespec64(wallclock);
+
+	cputime = timespec64_to_ns(&utime) + timespec64_to_ns(&stime);
+	pcpu = div64_u64(cputime * 100, wallclock);
+
+	len += scnprintf(msg + len, *msglen - len,
+			 /* task, PID, task state */
+			 "cmd: %s %d [%s] "
+			 /* rtime,    utime,      stime,      %cpu,  rss */
+			 "%llu.%02lur %llu.%02luu %llu.%02lus %llu%% %luk\n",
+			 tname,	__get_pid(p, tty),
+			 (char *)get_task_state_name(p),
+			 rtime.tv_sec, frac_sec(rtime.tv_nsec),
+			 utime.tv_sec, frac_sec(utime.tv_nsec),
+			 stime.tv_sec, frac_sec(stime.tv_nsec),
+			 pcpu, getRSSk(p->mm));
+
+out:
+	*msglen = len;
+	return 0;
+}
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 6616d4a0d41d..f2f4f48ea502 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -125,7 +125,7 @@ struct ktermios tty_std_termios = {	/* for the benefit of tty drivers  */
 	.c_oflag = OPOST | ONLCR,
 	.c_cflag = B38400 | CS8 | CREAD | HUPCL,
 	.c_lflag = ISIG | ICANON | ECHO | ECHOE | ECHOK |
-		   ECHOCTL | ECHOKE | IEXTEN,
+		   ECHOCTL | ECHOKE | IEXTEN | NOKERNINFO,
 	.c_cc = INIT_C_CC,
 	.c_ispeed = 38400,
 	.c_ospeed = 38400,
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 5dbd7c5afac7..e6ba6ce2efcb 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -49,71 +49,73 @@
 #define WERASE_CHAR(tty) ((tty)->termios.c_cc[VWERASE])
 #define LNEXT_CHAR(tty)	((tty)->termios.c_cc[VLNEXT])
 #define EOL2_CHAR(tty) ((tty)->termios.c_cc[VEOL2])
+#define STATUS_CHAR(tty) ((tty)->termios.c_cc[VSTATUS])
 
 #define _I_FLAG(tty, f)	((tty)->termios.c_iflag & (f))
 #define _O_FLAG(tty, f)	((tty)->termios.c_oflag & (f))
 #define _C_FLAG(tty, f)	((tty)->termios.c_cflag & (f))
 #define _L_FLAG(tty, f)	((tty)->termios.c_lflag & (f))
 
-#define I_IGNBRK(tty)	_I_FLAG((tty), IGNBRK)
-#define I_BRKINT(tty)	_I_FLAG((tty), BRKINT)
-#define I_IGNPAR(tty)	_I_FLAG((tty), IGNPAR)
-#define I_PARMRK(tty)	_I_FLAG((tty), PARMRK)
-#define I_INPCK(tty)	_I_FLAG((tty), INPCK)
-#define I_ISTRIP(tty)	_I_FLAG((tty), ISTRIP)
-#define I_INLCR(tty)	_I_FLAG((tty), INLCR)
-#define I_IGNCR(tty)	_I_FLAG((tty), IGNCR)
-#define I_ICRNL(tty)	_I_FLAG((tty), ICRNL)
-#define I_IUCLC(tty)	_I_FLAG((tty), IUCLC)
-#define I_IXON(tty)	_I_FLAG((tty), IXON)
-#define I_IXANY(tty)	_I_FLAG((tty), IXANY)
-#define I_IXOFF(tty)	_I_FLAG((tty), IXOFF)
-#define I_IMAXBEL(tty)	_I_FLAG((tty), IMAXBEL)
-#define I_IUTF8(tty)	_I_FLAG((tty), IUTF8)
-
-#define O_OPOST(tty)	_O_FLAG((tty), OPOST)
-#define O_OLCUC(tty)	_O_FLAG((tty), OLCUC)
-#define O_ONLCR(tty)	_O_FLAG((tty), ONLCR)
-#define O_OCRNL(tty)	_O_FLAG((tty), OCRNL)
-#define O_ONOCR(tty)	_O_FLAG((tty), ONOCR)
-#define O_ONLRET(tty)	_O_FLAG((tty), ONLRET)
-#define O_OFILL(tty)	_O_FLAG((tty), OFILL)
-#define O_OFDEL(tty)	_O_FLAG((tty), OFDEL)
-#define O_NLDLY(tty)	_O_FLAG((tty), NLDLY)
-#define O_CRDLY(tty)	_O_FLAG((tty), CRDLY)
-#define O_TABDLY(tty)	_O_FLAG((tty), TABDLY)
-#define O_BSDLY(tty)	_O_FLAG((tty), BSDLY)
-#define O_VTDLY(tty)	_O_FLAG((tty), VTDLY)
-#define O_FFDLY(tty)	_O_FLAG((tty), FFDLY)
-
-#define C_BAUD(tty)	_C_FLAG((tty), CBAUD)
-#define C_CSIZE(tty)	_C_FLAG((tty), CSIZE)
-#define C_CSTOPB(tty)	_C_FLAG((tty), CSTOPB)
-#define C_CREAD(tty)	_C_FLAG((tty), CREAD)
-#define C_PARENB(tty)	_C_FLAG((tty), PARENB)
-#define C_PARODD(tty)	_C_FLAG((tty), PARODD)
-#define C_HUPCL(tty)	_C_FLAG((tty), HUPCL)
-#define C_CLOCAL(tty)	_C_FLAG((tty), CLOCAL)
-#define C_CIBAUD(tty)	_C_FLAG((tty), CIBAUD)
-#define C_CRTSCTS(tty)	_C_FLAG((tty), CRTSCTS)
-#define C_CMSPAR(tty)	_C_FLAG((tty), CMSPAR)
-
-#define L_ISIG(tty)	_L_FLAG((tty), ISIG)
-#define L_ICANON(tty)	_L_FLAG((tty), ICANON)
-#define L_XCASE(tty)	_L_FLAG((tty), XCASE)
-#define L_ECHO(tty)	_L_FLAG((tty), ECHO)
-#define L_ECHOE(tty)	_L_FLAG((tty), ECHOE)
-#define L_ECHOK(tty)	_L_FLAG((tty), ECHOK)
-#define L_ECHONL(tty)	_L_FLAG((tty), ECHONL)
-#define L_NOFLSH(tty)	_L_FLAG((tty), NOFLSH)
-#define L_TOSTOP(tty)	_L_FLAG((tty), TOSTOP)
-#define L_ECHOCTL(tty)	_L_FLAG((tty), ECHOCTL)
-#define L_ECHOPRT(tty)	_L_FLAG((tty), ECHOPRT)
-#define L_ECHOKE(tty)	_L_FLAG((tty), ECHOKE)
-#define L_FLUSHO(tty)	_L_FLAG((tty), FLUSHO)
-#define L_PENDIN(tty)	_L_FLAG((tty), PENDIN)
-#define L_IEXTEN(tty)	_L_FLAG((tty), IEXTEN)
-#define L_EXTPROC(tty)	_L_FLAG((tty), EXTPROC)
+#define I_IGNBRK(tty)	  _I_FLAG((tty), IGNBRK)
+#define I_BRKINT(tty)	  _I_FLAG((tty), BRKINT)
+#define I_IGNPAR(tty)	  _I_FLAG((tty), IGNPAR)
+#define I_PARMRK(tty)	  _I_FLAG((tty), PARMRK)
+#define I_INPCK(tty)	  _I_FLAG((tty), INPCK)
+#define I_ISTRIP(tty)	  _I_FLAG((tty), ISTRIP)
+#define I_INLCR(tty)	  _I_FLAG((tty), INLCR)
+#define I_IGNCR(tty)	  _I_FLAG((tty), IGNCR)
+#define I_ICRNL(tty)	  _I_FLAG((tty), ICRNL)
+#define I_IUCLC(tty)	  _I_FLAG((tty), IUCLC)
+#define I_IXON(tty)	  _I_FLAG((tty), IXON)
+#define I_IXANY(tty)	  _I_FLAG((tty), IXANY)
+#define I_IXOFF(tty)	  _I_FLAG((tty), IXOFF)
+#define I_IMAXBEL(tty)	  _I_FLAG((tty), IMAXBEL)
+#define I_IUTF8(tty)	  _I_FLAG((tty), IUTF8)
+
+#define O_OPOST(tty)	  _O_FLAG((tty), OPOST)
+#define O_OLCUC(tty)	  _O_FLAG((tty), OLCUC)
+#define O_ONLCR(tty)	  _O_FLAG((tty), ONLCR)
+#define O_OCRNL(tty)	  _O_FLAG((tty), OCRNL)
+#define O_ONOCR(tty)	  _O_FLAG((tty), ONOCR)
+#define O_ONLRET(tty)	  _O_FLAG((tty), ONLRET)
+#define O_OFILL(tty)	  _O_FLAG((tty), OFILL)
+#define O_OFDEL(tty)	  _O_FLAG((tty), OFDEL)
+#define O_NLDLY(tty)	  _O_FLAG((tty), NLDLY)
+#define O_CRDLY(tty)	  _O_FLAG((tty), CRDLY)
+#define O_TABDLY(tty)	  _O_FLAG((tty), TABDLY)
+#define O_BSDLY(tty)	  _O_FLAG((tty), BSDLY)
+#define O_VTDLY(tty)	  _O_FLAG((tty), VTDLY)
+#define O_FFDLY(tty)	  _O_FLAG((tty), FFDLY)
+
+#define C_BAUD(tty)	  _C_FLAG((tty), CBAUD)
+#define C_CSIZE(tty)	  _C_FLAG((tty), CSIZE)
+#define C_CSTOPB(tty)	  _C_FLAG((tty), CSTOPB)
+#define C_CREAD(tty)	  _C_FLAG((tty), CREAD)
+#define C_PARENB(tty)	  _C_FLAG((tty), PARENB)
+#define C_PARODD(tty)	  _C_FLAG((tty), PARODD)
+#define C_HUPCL(tty)	  _C_FLAG((tty), HUPCL)
+#define C_CLOCAL(tty)	  _C_FLAG((tty), CLOCAL)
+#define C_CIBAUD(tty)	  _C_FLAG((tty), CIBAUD)
+#define C_CRTSCTS(tty)	  _C_FLAG((tty), CRTSCTS)
+#define C_CMSPAR(tty)	  _C_FLAG((tty), CMSPAR)
+
+#define L_ISIG(tty)	  _L_FLAG((tty), ISIG)
+#define L_ICANON(tty)	  _L_FLAG((tty), ICANON)
+#define L_XCASE(tty)	  _L_FLAG((tty), XCASE)
+#define L_ECHO(tty)	  _L_FLAG((tty), ECHO)
+#define L_ECHOE(tty)	  _L_FLAG((tty), ECHOE)
+#define L_ECHOK(tty)	  _L_FLAG((tty), ECHOK)
+#define L_ECHONL(tty)	  _L_FLAG((tty), ECHONL)
+#define L_NOFLSH(tty)	  _L_FLAG((tty), NOFLSH)
+#define L_TOSTOP(tty)	  _L_FLAG((tty), TOSTOP)
+#define L_ECHOCTL(tty)	  _L_FLAG((tty), ECHOCTL)
+#define L_ECHOPRT(tty)	  _L_FLAG((tty), ECHOPRT)
+#define L_ECHOKE(tty)	  _L_FLAG((tty), ECHOKE)
+#define L_FLUSHO(tty)	  _L_FLAG((tty), FLUSHO)
+#define L_PENDIN(tty)	  _L_FLAG((tty), PENDIN)
+#define L_IEXTEN(tty)	  _L_FLAG((tty), IEXTEN)
+#define L_EXTPROC(tty)	  _L_FLAG((tty), EXTPROC)
+#define L_NOKERNINFO(tty) _L_FLAG((tty), NOKERNINFO)
 
 struct device;
 struct signal_struct;
@@ -388,6 +390,9 @@ void __init n_tty_init(void);
 static inline void n_tty_init(void) { }
 #endif
 
+/* n_tty_status.c */
+extern int n_tty_get_status(struct tty_struct *tty, char *msg, size_t *msglen);
+
 /* tty_audit.c */
 #ifdef CONFIG_AUDIT
 void tty_audit_exit(void);
-- 
2.30.2