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

From: Kay Sievers
Date: Thu Jul 19 2012 - 05:39:14 EST

On Wed, Jul 18, 2012 at 7:56 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> On Wed, Jul 18, 2012 at 07:27:08PM +0200, Kay Sievers wrote:
>> On Wed, Jul 18, 2012 at 7:18 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> 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?
> Yes, that should work. Here is the prototype patch which stores 5 bits
> of flag and 3 bits of level in a byte. I have not tested it yet, but
> if you like the approach, I will test it.

> - u8 flags:5; /* internal record flags */
> - u8 level:3; /* syslog level */
> + u8 flags_level; /* 5 bit internal record flags, 3 bits syslog

Looks ok.

If we would swap the 5 + 3 bit field byte declaration, and add
__packed, we can still not rely on the level to be consistently the
lower 3 bits of the byte, right?

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