linux-kernel - Re: [PATCH v2 1/1] eventfd: implementation of EFD

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Message-ID: <5121EC47.2080402@250bpm.com>
Date:	Mon, 18 Feb 2013 09:54:31 +0100
From:	Martin Sustrik <sustrik@...bpm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Alexander Viro <viro@...iv.linux.org.uk>,
	Sha Zhengju <handai.szj@...bao.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Michael Kerrisk <mtk.manpages@...il.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Andy Lutomirski <luto@...capital.net>,
	Eric Wong <normalperson@...t.net>
Subject: Re: [PATCH v2 1/1] eventfd: implementation of EFD_MASK flag

On 14/02/13 23:54, Andrew Morton wrote:

>> +/*  On x86-64 keep the same binary layout as on i386. */
>> +#ifdef __x86_64__
>> +#define EVENTFD_MASK_PACKED __packed
>> +#else
>> +#define EVENTFD_MASK_PACKED
>> +#endif
>> +
>> +struct eventfd_mask {
>> +	__u32 events;
>> +	__u64 data;
>> +} EVENTFD_MASK_PACKED;
>
> The x86-64 specific thing is ugly.  I can find no explanation of why it
> was done, but it should go away.  You could make `events' a u64, or
> swap the order of the two fields and make the struct __packed on all
> architectures.
>
> Given that the size of the types is fixed, I see no compat issues here.

I've just copied how the definition is done for epoll_event. The comment 
there goes like this:

/*
  * On x86-64 make the 64bit structure have the same alignment as the
  * 32bit structure. This makes 32bit emulation easier.
  *
  * UML/x86_64 needs the same packing as x86_64
  */

If you still think I should remove the #ifdef, I am happy to do so.

Martin
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