On Mon, 6 Jan 2014 06:34:11 -0700
Matthew Flatt <mfl...@cs.utah.edu> wrote:
> At Mon, 6 Jan 2014 13:47:30 +0100, Manfred Lotz wrote:
> > On Mon, 6 Jan 2014 10:32:49 +0100
> > Manfred Lotz <manfred.l...@arcor.de> wrote:
> >
> > > I was to quick to state this is a solution as it is not a good
> > > idea if for example a socket file will be shown as a duplicate of
> > > normal file having size zero.
> > >
> > > For the time being I guess I have to look how to implement it
> > > using C stat call from Racket.
> > >
> > >
> >
> > To get into I tried the example in 'Indide Racket C API'/Overview
> >
> > I got:
> > compiled
> > compiled/native
> > compiled/native/amd64-linux
> > compiled/native/amd64-linux/3m
> > compiled/native/amd64-linux/3m/hi_rkt.so
> >
> >
> > Documentation says that it could be loaded like this:
> >
> > (require "hi.rkt")
> >
> >
> > Now my question: What would the content of hi.rkt be?
>
> The analogous source "hi.rkt" would be
>
> #lang racket/base
> (provide greeting)
> (define greeting "hello")
>
> but you don't actually create a "hi.rkt". Instead, the module loader
> substitutes "hit_rkt.so".
>
>
> Did you consider using `ffi/unsafe` instead of creating an extension?
> Using the FFI library is usually much easier and more portable.
> Unfortunately, the `stat` function, with its structure layout that
> varies across platforms, is more difficult to call via `ffi/unsafe`,
> but I would still do that instead of trying to write an extension.
>
To be honest, no. I've never did anything like this before. When I
found the extension stuff it looked quite good to me because of the
'hi' example.
Now I messed around with the FFI stuff. I tried out a small C programm
to double check if the stat struct has the right length. I'm not quite
sure if I got the internal name of the stat function right. At least I
still get a -1 from stat.
#lang racket
(require ffi/unsafe
ffi/unsafe/define)
(define-cstruct _STAT
((dev_t _long)
(ino_t _long)
(nlink_t _long)
(mode_t _int)
(uid_t _int)
(gid_t _int)
(pad0 _int)
(rdev_t _long)
(size_t _long)
(blksize_t _long)
(blkcnt_t _long)
(atime_t _long)
(atime_nsec_t _long)
(mtime_t _long)
(mtime_nsec_t _long)
(ctime_t _long)
(ctime_nsec_t _long)
(unused1 _long)
(unused2 _long)
(unused3 _long)))
(define-ffi-definer define-stats (ffi-lib "libc.so.6"))
(define-stats __xstat64 (_fun _string _STAT-pointer -> _int))
(define-stats __xstat (_fun _string _STAT-pointer -> _int))
(define (socket-exists f)
(define s (make-STAT 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0))
(__xstat64 f s))
(socket-exists "cstat.c")
However, I agree. If I get the struct stuff straight then for what I
want it is indeed easier to do the FFI stuff
--
Manfred
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