netdev - Re: [PATCH] net: Fix struct sock bitfield annotation

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Date:	Fri, 09 Oct 2009 00:54:08 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	vegard.nossum@...il.com, netdev@...r.kernel.org, mingo@...e.hu
Subject: Re: [PATCH] net: Fix struct sock bitfield annotation

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 09 Oct 2009 03:07:56 +0200

> Point is we should not lose 8 bytes with kmemcheck on or off.
> I believe kmemcheck macros are fine as they are.
> 
> When we have a structure with
> 
>         unsigned char           sk_shutdown : 2,
>                                 sk_no_check : 2,
>                                 sk_userlocks : 4;
>         unsigned char           sk_protocol;
>         unsigned short          sk_type;
> 
> Its pretty clear its *logically* a bitfield aggregation, or if you prefer :

I think from a practical standpoint, you are right.

But Vegard is right too, as we should be able to put the annotation
right next to the ":" statements.

So if you really want why don't you put the sk_protocol and
sk_type into the ":" block as you mentioned.

And then you can use Arnaldo's 'pahole' instead of the kludgy
offsetof() which doesn't work with bitfields :-)

I want the 8 bytes back just like you, but seperating the annotation
from the real C bitfields looks definitely wrong to me.
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