Re: [PATCH] Consolidate Linux readahead() implementations

[Yury Norov <ynorov@caviumnetworks.com>]

On Fri, Sep 23, 2016 at 11:24:32AM -0300, Adhemerval Zanella wrote:
> 
> 
> On 23/09/2016 11:11, Yury Norov wrote:
> > On Fri, Sep 23, 2016 at 10:32:35AM -0300, Adhemerval Zanella wrote:
> >>
> >> Indeed, unfortunately tile seems to get its own readahead definition.
> >> However I think it should not prevent us to use my previous strategy,
> >> we can follow the SH example for pread (where it adds a dummy argument
> >> before offset), and do something as:
> >>
> >> sysdeps/unix/sysv/linux/tile/readahead.c
> >>
> >> #include <sysdep.h>
> >>
> >> #ifndef _LP64
> >> /* Although tile 32-bit ABI passed 64-bit arguments in even registers,
> >>    readahead interface does not follow this convention.  */
> >> # undef __ALIGNMENT_ARG
> >> #endif
> >>
> >> #include <sysdeps/unix/sysv/linux/readhead.c>
> > 
> > Currently it looks like this to me (see below). If you think that separated file
> > is better than new option - I'm OK with it, but I think it's strange because in
> > other patches of series you introduce options (if I'm not mistake).
> 
> I prefer to not add any more __ASSUME macro until it is more general
> and for this specific case (tile seems the only supported ABI that
> implements readhead different than usual ABI).
> 
> > 
> > We also have 2 another implementations - in linux/wordsize-64/syscalls.list
> > and linux/mips/mips64/n32/syscalls.list.
> > 
> > I think wordsize-64 is safe to generalize, but I'm worry about mips64. If we'll
> > choose adding new options and so having a single file, it seems, we'll have to
> > add another option for mips64/n32, like this:
> 
> My understanding is mipc64n32 adds it on syscall list to avoid current
> default Linux implementation where it splits the off64_t (since mips64n32
> passes off64_t in only one register afaik).  I think it is safe here,
> since SYSCALL_LL64 for mips64n32 will correctly pass only one argument
> instead of splitting it.

OK. So for v2:
 - remove arm, mips, wordsize-64, powerpc implementations
 - generalize linux/readahead.c like below
 - add tile exception
 - remove all new __ASSUME 

If it's correct, I'll send new patch this evening or tomorrow.

Yury.

> >  ssize_t
> >  __readahead (int fd, off64_t offset, size_t count)
> >  {
> > -  return INLINE_SYSCALL (readahead, 4, fd,
> > -			 __LONG_LONG_PAIR ((off_t) (offset >> 32),
> > -					   (off_t) (offset & 0xffffffff)),
> > -			 count);
> > +  return INLINE_SYSCALL_CALL (readahead, fd, __ALIGNMENT_ARG
> > +			      SYSCALL_LL64 (offset));