Re: GNU Shepherd 0.10.3 released

["Ludovic Courtès" <ludo@gnu.org>]

Hello,

Tomas Volf <~@wolfsden.cz> skribis:

> Otherwise the shepherd would be stuck on shutdown waiting for process named
>
>     [mt76-tx phy0]
>
> to terminate with messages along the lines of:
>
>     shepherd[1]: waiting for process termination (processes left: (1 678))
>
> It is a kernel thread as far as I can tell (based on
> https://stackoverflow.com/a/12231039):
>
>     $ cd /proc/678
>     $ cat cmdline
>     $ readlink exe; echo $?
>     1
>
> Removing the module mt7921e stops the thread, so shepherd does not wait for it.

Ooooh.

Then I’m afraid this bug isn’t fixed yet because that code (“waiting for
process termination”) is currently in Guix, not in Shepherd.

However, ‘processes’, which is what is used here and which is defined in
(guix build syscalls), already checks for kernel threads, though it
does it differently than what I implemented in shepherd:

  (define (kernel? pid)
    "Return #t if PID designates a \"kernel thread\" rather than a normal
  user-land process."
    (let ((stat (call-with-input-file (format #f "/proc/~a/stat" pid)
                  (compose string-tokenize read-string))))
      ;; See proc.txt in Linux's documentation for the list of fields.
      (match stat
        ((pid tcomm state ppid pgrp sid tty_nr tty_pgrp flags min_flt
              cmin_flt maj_flt cmaj_flt utime stime cutime cstime
              priority nice num_thread it_real_value start_time
              vsize rss rsslim
              (= string->number start_code) (= string->number end_code) _ ...)
         ;; Got this obscure trick from sysvinit's 'killall5' program.
         (and (zero? start_code) (zero? end_code))))))

It would be great if you could check whether this approach works for
you.

(I had completely forgotten about this code.  Funny thing is this one
was inspired by sysvinit, whereas the one in Shepherd was inspired by
systemd.  A sign of times!)

Ludo’.