fcntl(F_RDAHEAD)

[Igor Sysoev]

On Mon, Sep 21, 2009 at 02:29:09PM +0300, Kostik Belousov wrote:

> > > What I dislike about the patch is the new kernel-private flag that is
> > > eaten from the open(2) flags namespace. We do already have FHASLOCK,
> > > so far the only such flag.
> > 
> > We can change
> >   int    f_seqcount;
> > to
> >   u_int  f_seqcount;
> > 
> > and can use highest bit instead of O_READAHEAD: anyway f_seqcount is shifted
> > to 16 bits left.
> 
> Or do the same trick as was done for FHASLOCK and override some flag that
> is not saved after open, see FMASK.

Probably, you meant FPOSIXSHM, but not FHASLOCK:

/*
 * We are out of bits in f_flag (which is a short).  However,
 * the flag bits not set in FMASK are only meaningful in the
 * initial open syscall.  Those bits can thus be given a
 * different meaning for fcntl(2).
 */
#if __BSD_VISIBLE

/*
 * Set by shm_open(3) to get automatic MAP_ASYNC behavior
 * for POSIX shared memory objects (which are otherwise
 * implemented as plain files).
 */
#define FPOSIXSHM       O_NOFOLLOW
#endif



-- 
Igor Sysoev
http://sysoev.ru/en/