linux-kernel - Re: [RFC][PATCH] bitfields API

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Message-ID: <19f34abd0808281218p725184fdrd7ac655db0a20c8d@mail.gmail.com>
Date:	Thu, 28 Aug 2008 21:18:33 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Alexey Dobriyan" <adobriyan@...il.com>
Cc:	"David Miller" <davem@...emloft.net>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Pekka Enberg" <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] bitfields API

On Thu, Aug 28, 2008 at 9:05 PM, Alexey Dobriyan <adobriyan@...il.com> wrote:
> On Thu, Aug 28, 2008 at 08:46:43PM +0200, Vegard Nossum wrote:
>> On Thu, Aug 28, 2008 at 8:40 PM, Alexey Dobriyan <adobriyan@...il.com> wrote:
>> > On Thu, Aug 28, 2008 at 08:32:23PM +0200, Vegard Nossum wrote:
>> >> How do you feel about this patch? It's all about making kmemcheck more
>> >> useful... and not much else. Does it have any chance of entering the
>> >> kernel along with kmemcheck (when/if that happens)?
>> >
>> > DEFINE_BITFIELD is horrible.
>> >
>> >> @@ -285,11 +286,12 @@ struct sk_buff {
>> >>               };
>> >>       };
>> >>       __u32                   priority;
>> >> -     __u8                    local_df:1,
>> >> +     DEFINE_BITFIELD(__u8,   flags1,
>> >> +                             local_df:1,

[...]

>> Would it help (to make this less
>> horrible) to omit the type declaration and have just the bitfield
>> members as arguments to the macro?
>
> Or you can parse instruction stream a bit more.

I think we have different opinions of what exactly constitutes "horrible" :-P

Your suggestion would have made sense if I was a company of 10
developers who could import all of valgrind source code (including
opcode decoder and instruction emulator) into the kernel. But I only
writing kmemcheck in my free time, so this will never happen. Or.. at
least I will not do it. Of course, kmemcheck, valgrind/memcheck, and
indeed the kernel itself are all open source, so anybody could do it.
And if you want to submit patches yourself, the effort will be welcome
:-)

In the mean-time, I am looking for an acceptable solution. Other
debugging features use helper annotations too. But I am pretty sure
that the immediate solution will not include parsing the instruction
stream a bit more.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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