Re: [RFC 01/32] fs: introduce new 'struct inode_time'

Arnd Bergmann
2014-05-31T14:56:31Z

On Saturday 31 May 2014 10:39:02 Andreas Schwab wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> writes:
>
> > Hi Arnd,
> >
> > On Fri, May 30, 2014 at 10:01 PM, Arnd Bergmann <arnd@arndb.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?

It was a mistake on my side, as I didn't know about that rule and
meant write 'unsigned int' really. Also, I always have a bad feeling
about using bitfields in general.

Arnd