linux-kernel - Re: [PATCH] printk: Export struct log size and member offsets through vmcoreinfo

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Message-ID: <CAPXgP12PioibfQhtAB0fCzL1MXmZvfvQqOGu_ZM0D8Sx4Vq7+w@mail.gmail.com>
Date:	Wed, 18 Jul 2012 19:27:08 +0200
From:	Kay Sievers <kay@...y.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartmann <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] printk: Export struct log size and member offsets through vmcoreinfo

On Wed, Jul 18, 2012 at 7:18 PM, Vivek Goyal <vgoyal@...hat.com> wrote:

> Currently I am not exporting log "level" info as that is a bitfield and
> offsetof() bitfields can't be calculated.

We could make the level the lower 3 bits of the byte, export the byte,
and define that only 3 bits of the byte are valid? Would that help?

>  kernel/printk.c |    9 +++++++++
>  1 file changed, 9 insertions(+)

> +       /*
> +        * Export struct log size and field offsets. User space tools can
> +        * parse it and detect any changes to structure down the line.
> +        */
> +       VMCOREINFO_STRUCT_SIZE(log);
> +       VMCOREINFO_OFFSET(log, ts_nsec);
> +       VMCOREINFO_OFFSET(log, len);
> +       VMCOREINFO_OFFSET(log, text_len);
> +       VMCOREINFO_OFFSET(log, dict_len);

Ah, nice, that's how you handle exporting structures, it was still on
my list, to find out how all that should look like.

Cc:ing Greg, to pick it up.

Thanks a lot for taking care of it,
Kay
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