Toggle quote (54 lines)
> Date: Mon, 29 Jan 2024 17:31:33 +0100
> From: Ludovic Courtès <ludo@gnu.org>
> To: guix-devel@gnu.org
> Subject: Re: GNU Shepherd 0.10.3 released
>
> Hi,
>
> Tomas Volf <~@wolfsden.cz> skribis:
>
> > Ah, that code indeed returns #f for the pid in question:
> >
> > scheme@(guix-user)> ((@@ (guix build syscalls) kernel?) 688)
> > $1 = #f
> >
> > The stat file:
> >
> > $ cat /proc/688/stat
> > 688 (mt76-tx phy0) S 2 0 0 0 -1 2129984 0 0 0 0 0 0 0 0 -2 0 1 0 964 0 0 18446744073709551615 0 0 0 0 0 0 0 2147483647 0 0 0 0 17 5 1 1 0 0 0 0 0 0 0 0 0 0 0
> >
> > So the start_code is not zero (I would guess it is -1). I have no idea what
> > that means though.
>
> What about this method (from shepherd)?
>
> --8<---------------cut here---------------start------------->8---
> (define (linux-process-flags pid)
> "Return the process flags of @var{pid} (or'd @code{PF_} constants), assuming
> the Linux /proc file system is mounted; raise a @code{system-error} exception
> otherwise."
> (call-with-input-file (string-append "/proc/" (number->string pid)
> "/stat")
> (lambda (port)
> (define line
> (get-string-all port))
>
> ;; Parse like systemd's 'is_kernel_thread' function.
> (let ((offset (string-index line #\)))) ;offset past 'tcomm' field
> (match (and offset
> (string-tokenize (string-drop line (+ offset 1))))
> ((state ppid pgrp sid tty-nr tty-pgrp flags . _)
> (or (string->number flags) 0))
> (_
> 0))))))
>
> ;; Per-process flag defined in <linux/sched.h>.
> (define PF_KTHREAD #x00200000) ;I am a kernel thread
>
> (define (linux-kernel-thread? pid)
> "Return true if @var{pid} is a Linux kernel thread."
> (= PF_KTHREAD (logand (linux-process-flags pid) PF_KTHREAD)))
> --8<---------------cut here---------------end--------------->8---
>
> If it works better, we can use that in syscalls.scm as well.
Yes, that does seem to work:
scheme@(guile-user)> ,use (ice-9 match)
scheme@(guile-user)> ,use (ice-9 textual-ports)
scheme@(guile-user)> (define (linux-process-flags pid)
"Return the process flags of @var{pid} (or'd @code{PF_} constants), assuming
the Linux /proc file system is mounted; raise a @code{system-error} exception
otherwise."
(call-with-input-file (string-append "/proc/" (number->string pid)
"/stat")
(lambda (port)
(define line
(get-string-all port))
;; Parse like systemd's 'is_kernel_thread' function.
(let ((offset (string-index line #\)))) ;offset past 'tcomm' field
(match (and offset
(string-tokenize (string-drop line (+ offset 1))))
((state ppid pgrp sid tty-nr tty-pgrp flags . _)
(or (string->number flags) 0))
(_
0))))))
scheme@(guile-user)> ;; Per-process flag defined in <linux/sched.h>.
(define PF_KTHREAD #x00200000) ;I am a kernel thread
scheme@(guile-user)> (define (linux-kernel-thread? pid)
"Return true if @var{pid} is a Linux kernel thread."
(= PF_KTHREAD (logand (linux-process-flags pid) PF_KTHREAD)))
scheme@(guile-user)> (linux-kernel-thread? 685)
$5 = #t
Tomas
--
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.
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