Subject: [wishlist] scheme level mmap

From: Matt Wette <[email-masked]>
Date: Fri, 21 Jul 2017 06:39:32 -0700

There was an implicit request on the user-guile mailing list (20 Jul 2017) to provide a scheme language call to mmap.

I am working on a prototype and will post when I get a simple case working.  Here is non-working code so far:

Currently I have this in a file “mmap.c” and #including into filesys.c.

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#ifdef HAVE_SYS_MMAN_H
#  include <sys/mman.h>
#endif

#include "libguile/_scm.h"
#include "libguile/smob.h"
#include "libguile/fdes-finalizers.h"
#include "libguile/feature.h"

SCM_API SCM scm_mmap (SCM addr, SCM len, SCM prot, SCM flags, SCM fd,
		      SCM offset);
SCM_API SCM scm_munmap (SCM addr, SCM len);

#if defined(HAVE_SYS_MMAN_H) && defined(HAVE_MAP_ANONYMOUS)
// python mmap makes the last four args optional
// should use fd=-1 default on mac
SCM_DEFINE (scm_mmap, "mmap", 6, 0, 0, 
            (SCM addr, SCM len, SCM prot, SCM flags, SCM fd, SCM offset),
	    "See the man page. returns a foreign pointer which one would"
	    "ordinarily convert to bytevector using pointer->bytevector.  "
	    "Note that the region returned by mmap is not (?) searched "
	    "by the garbage collector."
	    "@example\n(define reg\n (pointer->bytevector\n  "
	    "(mmap %void-pointer #x10000 (logior PROT_READ PROT_WRITE) "
	    "MAP_ANON -1 0) #x1000))"
	    "@end example"
	    )
#define FUNC_NAME s_scm_mmap
{
  void *c_mem, *c_addr;
  size_t c_len;
  int c_prot, c_flags, c_fd;
  scm_t_off c_offset;
  SCM ret;

  SCM_VALIDATE_POINTER (1, addr);
  
  c_addr = (void *) SCM_POINTER_VALUE (addr);
  c_len = scm_to_size_t (len);
  c_prot = scm_to_int (prot);
  c_flags = scm_to_int (flags);
  c_fd = scm_to_int (fd);
  c_offset = SCM_UNBNDP (offset) ? 0: scm_to_off_t (offset);
  
  c_mem = mmap(c_addr, c_len, c_prot, c_flags, c_fd, c_offset);

  ret = scm_from_pointer (c_mem, NULL);
  return ret;
}

#undef FUNC_NAME
SCM_DEFINE (scm_munmap, "munmap", 2, 0, 0, 
            (SCM addr, SCM len),
	    "See the man page. Given foreign pointer unmap."
	    )
#define FUNC_NAME s_scm_munmap
{
  void *c_addr;
  size_t c_len;
  int c_res;
  SCM res;

  SCM_VALIDATE_POINTER (1, addr);
  
  c_addr = (void *) SCM_POINTER_VALUE (addr);
  c_len = scm_to_size_t (len);

  c_res = munmap(c_addr, c_len);
  res = scm_from_int (c_res);
  return res;
}
#endif /* HAVE_SYS_MMAN_H */

#if defined(HAVE_SYS_MMAN_H) && defined(HAVE_MAP_ANONYMOUS)

#define MMAP_DEFS					\
  scm_c_define ("PROT_NONE", scm_from_int (PROT_NONE)); \
  scm_c_define ("PROT_READ", scm_from_int (PROT_READ)); \
  scm_c_define ("PROT_WRITE", scm_from_int (PROT_WRITE)); \
  scm_c_define ("PROT_EXEC", scm_from_int (PROT_EXEC)); \
  \
  scm_c_define ("MAP_ANONYMOUS", scm_from_int (MAP_ANONYMOUS)); \
  scm_c_define ("MAP_ANON", scm_from_int (MAP_ANON)); \
  scm_c_define ("MAP_FILE", scm_from_int (MAP_FILE)); \
  scm_c_define ("MAP_FIXED", scm_from_int (MAP_FIXED)); \
  scm_c_define ("MAP_HASSEMAPHORE", scm_from_int (MAP_HASSEMAPHORE)); \
  scm_c_define ("MAP_PRIVATE", scm_from_int (MAP_PRIVATE)); \
  scm_c_define ("MAP_SHARED", scm_from_int (MAP_SHARED)); \
  scm_c_define ("MAP_NOCACHE", scm_from_int (MAP_NOCACHE))

#else
#define MMAP_DEFS /* */
#endif /* HAVE_SYS_MMAN_H */