linux-kernel - Re: [GIT pull] printk updates for 4.15

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Date:   Wed, 15 Nov 2017 00:22:45 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Mark Salyzyn <salyzyn@...roid.com>, Petr Mladek <pmladek@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Prarit Bhargava <prarit@...hat.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [GIT pull] printk updates for 4.15

On Tue, 14 Nov 2017, Linus Torvalds wrote:
> On Tue, Nov 14, 2017 at 3:04 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > True. I already replaced all of them except this one:
> >
> > @@ -1022,6 +1026,7 @@ void log_buf_vmcoreinfo_setup(void)
> >          */
> >         VMCOREINFO_STRUCT_SIZE(printk_log);
> >         VMCOREINFO_OFFSET(printk_log, ts_nsec);
> > +       VMCOREINFO_OFFSET(printk_log, ts);
> >         VMCOREINFO_OFFSET(printk_log, len);
> >         VMCOREINFO_OFFSET(printk_log, text_len);
> >         VMCOREINFO_OFFSET(printk_log, dict_len);
> >
> > If I remove ts_nsec completely, then the VMCORE info changes and that would
> > break existing tools because they search for ts_nsec and fail....
> 
> Dear god, that's nasty.
> 
> I agree that the vmcore info name probably needs to be retained, but
> maybe we could just do that with
> 
> #define VMCOREINFO_FIELD_AND_OFFSET(name, field, offset) \
>         vmcoreinfo_append_str("OFFSET(%s.%s)=%lu\n", name, field, offset)
> 
> and then do
> 
>   #define VMCOREINFO_OFFSET(name, field) \
>         VMCOREINFO_FIELD_AND_OFFSET(#name, #field, \
>                 (unsigned long)offsetof(struct name, offset))
> 
> and for that ts_nsec you can then do
> 
>    /* ts.mono used to be called "ts_nsec" */
>    VMCOREINFO_FIELD_AND_OFFSET("printk_log", "ts_nsec",
>         (unsigned long)offsetof(struct printk_log, ts.mono))
> 
> or something.
> 
> And I may obviously have messed that all up, I wrote it all in the
> email client, so it's more pseudo-code than anything else.
> 
> But it looks pretty straight-forward conceptually, and would make it
> pretty clear what is going on, no?

That should work. I'll try that tomorrow with brain awake.

Thanks,

	tglx