linux-kernel - Re: [PATCH v5 03/15] sched.h: introduce TASK_COMM_LEN

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Message-ID: <CALOAHbCu5vXT1DB+d-sv6r2ncBohnqry2uK9R4rYSvbHoVPLOg@mail.gmail.com>
Date:   Fri, 22 Oct 2021 14:23:27 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Peter Ziljstra <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Qiang Zhang <qiang.zhang@...driver.com>,
        robdclark <robdclark@...omium.org>,
        Christian Brauner <christian@...uner.io>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "linux-perf-use." <linux-perf-users@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        kernel test robot <oliver.sang@...el.com>,
        kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH v5 03/15] sched.h: introduce TASK_COMM_LEN_16

On Fri, Oct 22, 2021 at 5:55 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Wed, Oct 20, 2021 at 8:45 PM Yafang Shao <laoar.shao@...il.com> wrote:
> >
> > There're many hard-coded 16 used to store task comm in the kernel, that
> > makes it error prone if we want to change the value of TASK_COMM_LEN. A
> > new marco TASK_COMM_LEN_16 is introduced to replace these old ones, then
> > we can easily grep them.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Petr Mladek <pmladek@...e.com>
> > ---
> >  include/linux/sched.h | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index c1a927ddec64..62d5b30d310c 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -274,6 +274,8 @@ struct task_group;
> >
> >  #define get_current_state()    READ_ONCE(current->__state)
> >
> > +/* To replace the old hard-coded 16 */
> > +#define TASK_COMM_LEN_16               16
> >  /* Task command name length: */
> >  #define TASK_COMM_LEN                  16
>
> Can we please convert these two constants into enum? That will allow
> BPF applications to deal with such kernel change more easily because
> these constants will now be available as part of kernel BTF.
>
> Something like this should be completely equivalent for all the kernel uses:
>
> enum {
>     TASK_COMM_LEN = 16,
>     TASK_COMM_LEN_16 = 16,
> };
>
> When later TASK_COMM_LEN is defined as = 24, BPF applications will be
> able to deal with that by querying BTF through BPF CO-RE.
>

Sure. I will convert it to enum.


-- 
Thanks
Yafang