On Mon, Jan 03, 2022 at 10:19:56AM -0800, Walt Drummond wrote:
> Support TTY VSTATUS character, NOKERNINFO local control bit and the
> signal SIGINFO, all as in 4.3BSD.
> 
> Signed-off-by: Walt Drummond <walt@drummond.us>
> ---
>  arch/x86/include/asm/signal.h       |   2 +-
>  arch/x86/include/uapi/asm/signal.h  |   4 +-
>  drivers/tty/Makefile                |   2 +-
>  drivers/tty/n_tty.c                 |  21 +++++
>  drivers/tty/tty_io.c                |  10 ++-
>  drivers/tty/tty_ioctl.c             |   4 +
>  drivers/tty/tty_status.c            | 135 ++++++++++++++++++++++++++++
>  fs/proc/array.c                     |  29 +-----
>  include/asm-generic/termios.h       |   4 +-
>  include/linux/sched.h               |  52 ++++++++++-
>  include/linux/signal.h              |   4 +
>  include/linux/tty.h                 |   8 ++
>  include/uapi/asm-generic/ioctls.h   |   2 +
>  include/uapi/asm-generic/signal.h   |   6 +-
>  include/uapi/asm-generic/termbits.h |  34 +++----
>  15 files changed, 264 insertions(+), 53 deletions(-)
>  create mode 100644 drivers/tty/tty_status.c
> 
> <...>
> 
> diff --git a/drivers/tty/tty_status.c b/drivers/tty/tty_status.c
> new file mode 100644
> index 000000000000..a9600f5bd48c
> --- /dev/null
> +++ b/drivers/tty/tty_status.c
> @@ -0,0 +1,135 @@
> +// SPDX-License-Identifier: GPL-1.0+
> +/*
> + * tty_status.c --- implements VSTATUS and TIOCSTAT from BSD4.3/4.4
> + *
> + */
> +
> +#include <linux/sched.h>
> +#include <linux/mm.h>
> +#include <linux/tty.h>
> +#include <linux/sched/cputime.h>
> +#include <linux/sched/loadavg.h>
> +#include <linux/pid.h>
> +#include <linux/slab.h>
> +#include <linux/math64.h>
> +
> +#define MSGLEN (160 + TASK_COMM_LEN)
> +
> +inline unsigned long getRSSk(struct mm_struct *mm)
> +{
> +	if (mm == NULL)
> +		return 0;
> +	return get_mm_rss(mm) * PAGE_SIZE / 1024;
> +}
> +
> +inline long nstoms(long l)
> +{
> +	l /= NSEC_PER_MSEC * 10;
> +	if (l < 10)
> +		l *= 10;
> +	return l;
> +}
> +
> +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;
> +}
> +
> +struct task_struct *pick_process(struct pid *pgrp)
> +{
> +	struct task_struct *p, *winner = NULL;
> +
> +	read_lock(&tasklist_lock);
> +	do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
> +		winner = compare(p, winner);
> +	} while_each_pid_task(pgrp, PIDTYPE_PGID, p);
> +	read_unlock(&tasklist_lock);
> +
> +	return winner;
> +}
> +
> +int tty_status(struct tty_struct *tty)
> +{
> +	char tname[TASK_COMM_LEN];
> +	unsigned long loadavg[3];
> +	uint64_t pcpu, cputime, wallclock;
> +	struct task_struct *p;
> +	struct rusage rusage;
> +	struct timespec64 utime, stime, rtime;
> +	char msg[MSGLEN] = {0};
> +	int len = 0;
> +
> +	if (tty == NULL)
> +		return -ENOTTY;
> +
> +	get_avenrun(loadavg, FIXED_1/200, 0);
> +	len += scnprintf((char *)&msg[len], MSGLEN - len, "load: %lu.%02lu  ",
> +		       LOAD_INT(loadavg[0]), LOAD_FRAC(loadavg[0]));
> +
> +	if (tty->ctrl.session == NULL) {
> +		len += scnprintf((char *)&msg[len], MSGLEN - len,
> +				 "not a controlling terminal");
> +		goto print;
> +	}
> +
> +	if (tty->ctrl.pgrp == NULL) {
> +		len += scnprintf((char *)&msg[len], MSGLEN - len,
> +				 "no foreground process group");
> +		goto print;
> +	}
> +
> +	p = pick_process(tty->ctrl.pgrp);
> +	if (p == NULL) {
> +		len += scnprintf((char *)&msg[len], MSGLEN - len,
> +				 "empty foreground process group");
> +		goto print;
> +	}
> +
> +	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((char *)&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",
> +			 tname,	task_pid_vnr(p), (char *)get_task_state_name(p),

task_pid_vnr(p) returns the PID of p in the PID namespace of current:

  pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
                          struct pid_namespace *ns)
  {
          pid_t nr = 0;
  
          rcu_read_lock();
          if (!ns)
                  ns = task_active_pid_ns(current);
          nr = pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
          rcu_read_unlock();
  
          return nr;
  }
  struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
  {
          return ns_of_pid(task_pid(tsk));
  }
  static inline pid_t task_pid_vnr(struct task_struct *tsk)
  {
          return __task_pid_nr_ns(tsk, PIDTYPE_PID, NULL); 
  }

At this point current is an arbitrary kernel worker thread, not p. Most
likely we need another helper function in <linux/sched.h>.

> +			 rtime.tv_sec, nstoms(rtime.tv_nsec),
> +			 utime.tv_sec, nstoms(utime.tv_nsec),
> +			 stime.tv_sec, nstoms(stime.tv_nsec),
> +			 pcpu, getRSSk(p->mm));
> +
> +print:
> +	len += scnprintf((char *)&msg[len], MSGLEN - len, "\r\n");
> +	tty_write_message(tty, msg);
> +
> +	return 0;
> +}
> 
> <...>
> 
> -- 
> 2.30.2
>