linux-kernel - Re: [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit offset macro

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Message-ID: <4BE7F22E.9070504@oss.ntt.co.jp>
Date:	Mon, 10 May 2010 20:46:54 +0900
From:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>,
	Avi Kivity <avi@...hat.com>, mtosatti@...hat.com,
	agraf@...e.de, fernando@....ntt.co.jp, kvm@...r.kernel.org,
	kvm-ppc@...r.kernel.org, kvm-ia64@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, benh@...nel.crashing.org, paulus@...ba.org,
	linuxppc-dev@...abs.org, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit
 offset macro

(2010/05/06 22:38), Arnd Bergmann wrote:
> On Wednesday 05 May 2010, Takuya Yoshikawa wrote:
>> Date:
>> Yesterday 04:59:24
>>> That's why the bitmaps are defined as little endian u64 aligned, even on
>>> big endian 32-bit systems.  Little endian bitmaps are wordsize agnostic,
>>> and u64 alignment ensures we can use long-sized bitops on mixed size
>>> systems.
>
> Ok, I see.
>
>> There was a suggestion to propose set_le_bit_user() kind of macros.
>> But what I thought was these have a constraint you two explained and seemed to be
>> a little bit specific to some area, like KVM.
>>
>> So I decided to propose just the offset calculation macro.
>
> I'm not sure I understand how this macro is going to be used though.
> If you are just using this in kernel space, that's fine, please go for
> it.

Yes, I'm just using in kernel space: qemu has its own endian related helpers.

So if you allow us to place this macro in asm-generic/bitops/* it will help us.

Avi, what do you think? Do you want to place it in kvm.h ?


>
> However, if the intention is to use the same macro in user space, putting
> it into asm-generic/bitops/* is not going to help, because those headers
> are not available in user space, and I wouldn't want to change that.
>
> The definition of the macro is not part of the ABI, so just duplicate
> it in KVM if you need it there.
>
> 	Arnd

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