linux-kernel - Re: [PATCH 2/8] readahead: state based method routines: explicitly embed class_new/class

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Message-Id: <20070128111104.789cbd07.randy.dunlap@oracle.com>
Date:	Sun, 28 Jan 2007 11:11:04 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	7eggert@....de
Cc:	Fengguang Wu <wfg@...l.ustc.edu.cn>, Andrew Morton <akpm@...l.org>,
	Martin Peschke <mp3@...ibm.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/8] readahead: state based method routines: explicitly
 embed class_new/class_old inside flags

On Sat, 27 Jan 2007 13:01:08 +0100 Bodo Eggert wrote:

> Fengguang Wu <wfg@...l.ustc.edu.cn> wrote:
> 
> > The new/old ra class were implicitly stored in low bits of
> > file_ra_state.flags. Now make the data structure obvious, and remove the
> > coding tricks.
> 
> > +++ linux-2.6.20-rc4-mm1/include/linux/fs.h
> 
> > -     unsigned long flags;    /* RA_FLAG_xxx | ra_class_old | ra_class_new */
> > +     union {
> > +             unsigned long   flags;  /* RA_FLAG_xxx | class_old | class_new */
> > +             struct {
> > +                     u8      class_new;
> > +                     u8      class_old;
> 
> This doesn't work on big endiam machines, does it?
> 
> IMO you should use a bitfield instead.

Or "use bit masks instead" since

"The order of allocation of bit-fields within a unit (high-order to
low-order or low-order to high-order) is implementation-defined."

---
~Randy
-
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