linux-kernel - Re: [RFC 01/32] fs: introduce new 'struct inode

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Message-ID: <CAMuHMdXPQQpu_6k+Y6o=1u-u9EkkanKdGYp6-=BavyYHUH3AuA@mail.gmail.com>
Date:	Sat, 31 May 2014 15:19:48 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Andreas Schwab <schwab@...ux-m68k.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	"Joseph S. Myers" <joseph@...esourcery.com>,
	John Stultz <john.stultz@...aro.org>,
	Christoph Hellwig <hch@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ley Foon Tan <lftan@...era.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC 01/32] fs: introduce new 'struct inode_time'

Hi Andreas,

On Sat, May 31, 2014 at 10:39 AM, Andreas Schwab <schwab@...ux-m68k.org> wrote:
> Geert Uytterhoeven <geert@...ux-m68k.org> writes:
>
>> Hi Arnd,
>>
>> On Fri, May 30, 2014 at 10:01 PM, Arnd Bergmann <arnd@...db.de> wrote:
>>> + * The variant using bit fields is less efficient to access, but
>>> + * small and has a wider range as the 32-bit one, plus it keeps
>>> + * the signedness of the original timespec.
>>> + */
>>> +struct inode_time {
>>> +       long long       tv_sec  : 34;
>>> +       int             tv_nsec : 30;
>>> +};
>>
>> Don't you need 31 bits for tv_nsec, to accommodate for the sign bit?
>> I know you won't really store negative numbers there, but storing a large
>> positive number will become negative on read out, won't it?
>
> Only if the int bitfield is signed.  Bitfields are weird, aren't they? :-)

"int" is signed, right? Or do you mean a bitfield needs an explicit "signed"
keyword to be signed?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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