linux-kernel - Re: [PATCH v1 1/3] printk: honor the max_reason field in kmsg

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Date:   Mon, 4 May 2020 14:40:49 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        James Morris <jmorris@...ei.org>,
        Sasha Levin <sashal@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        anton@...msg.org, ccross@...roid.com,
        Tony Luck <tony.luck@...el.com>, robh+dt@...nel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v1 1/3] printk: honor the max_reason field in kmsg_dumper

Thank Kees, I think it is a little cleaner this way.

Thank you,
Pasha


On Mon, May 4, 2020 at 2:12 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, May 04, 2020 at 01:15:00PM -0400, Steven Rostedt wrote:
> > On Sat,  2 May 2020 10:35:53 -0400
> > Pavel Tatashin <pasha.tatashin@...een.com> wrote:
> >
> > > kmsg_dump() allows to dump kmesg buffer for various system events: oops,
> > > panic, reboot, etc. It provides an interface to register a callback call
> > > for clients, and in that callback interface there is a field "max_reason"
> > > which gets ignored unless always_kmsg_dump is passed as kernel parameter.
> > >
> > > Allow clients to decide max_reason, and keep the current behavior when
> > > max_reason is not set.
> > >
> > > Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
> > > ---
> > >  include/linux/kmsg_dump.h |  1 +
> > >  kernel/printk/printk.c    | 16 +++++++++-------
> > >  2 files changed, 10 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
> > > index 2e7a1e032c71..c0d703b7ce38 100644
> > > --- a/include/linux/kmsg_dump.h
> > > +++ b/include/linux/kmsg_dump.h
> > > @@ -28,6 +28,7 @@ enum kmsg_dump_reason {
> > >     KMSG_DUMP_RESTART,
> > >     KMSG_DUMP_HALT,
> > >     KMSG_DUMP_POWEROFF,
> > > +   KMSG_DUMP_MAX = KMSG_DUMP_POWEROFF
> >
> > Hmm, I didn't realize that enums were allowed to have duplicates. That can
> > usually screw up logic. I would recommend making that a define afterward.
> >
> > #define KMSG_DUMP_MAX KMSG_DUMP_POWEROFF
> >
> > As is done in other locations of the kernel.
>
> I've seen it also be the last item in an enum, then comparisons can just
> do "< KMSG_DUMP_MAX" instead of "<= KMSG_DUMP_MAX".
>
> --
> Kees Cook