mmap-sup.c

早期freebsd实现

/* Support for an sbrk-like function that uses mmap.
   Copyright 1992 Free Software Foundation, Inc.

   Contributed by Fred Fish at Cygnus Support.   [e-mail]

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

#if defined(HAVE_MMAP)

#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>

#ifndef SEEK_SET
#define SEEK_SET 0
#endif

#include "mmalloc.h"

extern int munmap PARAMS ((caddr_t, size_t));	/* Not in any header file */

/* Cache the pagesize for the current host machine.  Note that if the host
   does not readily provide a getpagesize() function, we need to emulate it
   elsewhere, not clutter up this file with lots of kluges to try to figure
   it out. */

static size_t pagesize;
extern int getpagesize PARAMS ((void));

#define PAGE_ALIGN(addr) (caddr_t) (((long)(addr) + pagesize - 1) & \
				    ~(pagesize - 1))

/*  Get core for the memory region specified by MDP, using SIZE as the
    amount to either add to or subtract from the existing region.  Works
    like sbrk(), but using mmap(). */

PTR
__mmalloc_mmap_morecore (mdp, size)
  struct mdesc *mdp;
  int size;
{
  PTR result = NULL;
  off_t foffset;	/* File offset at which new mapping will start */
  size_t mapbytes;	/* Number of bytes to map */
  caddr_t moveto;	/* Address where we wish to move "break value" to */
  caddr_t mapto;	/* Address we actually mapped to */
  char buf = 0;		/* Single byte to write to extend mapped file */

  if (pagesize == 0)
    {
      pagesize = getpagesize ();
    }
  if (size == 0)
    {
      /* Just return the current "break" value. */
      result = mdp -> breakval;
    }
  else if (size < 0)
    {
      /* We are deallocating memory.  If the amount requested would cause
	 us to try to deallocate back past the base of the mmap'd region
	 then do nothing, and return NULL.  Otherwise, deallocate the
	 memory and return the old break value. */
      if (mdp -> breakval + size >= mdp -> base)
	{
	  result = (PTR) mdp -> breakval;
	  mdp -> breakval += size;
	  moveto = PAGE_ALIGN (mdp -> breakval);
	  munmap (moveto, (size_t) (mdp -> top - moveto));
	  mdp -> top = moveto;
	}
    }
  else
    {
      /* We are allocating memory.  Make sure we have an open file
	 descriptor and then go on to get the memory. */
      if (mdp -> fd < 0)
	{
	  result = NULL;
	}
      else if (mdp -> breakval + size > mdp -> top)
	{
	  /* The request would move us past the end of the currently
	     mapped memory, so map in enough more memory to satisfy
	     the request.  This means we also have to grow the mapped-to
	     file by an appropriate amount, since mmap cannot be used
	     to extend a file. */
	  moveto = PAGE_ALIGN (mdp -> breakval + size);
	  mapbytes = moveto - mdp -> top;
	  foffset = mdp -> top - mdp -> base;
	  /* FIXME:  Test results of lseek() and write() */
	  lseek (mdp -> fd, foffset + mapbytes - 1, SEEK_SET);
	  write (mdp -> fd, &buf, 1);
	  mapto = mmap (mdp -> top, mapbytes, PROT_READ | PROT_WRITE,
			MAP_SHARED | MAP_FIXED, mdp -> fd, foffset);
	  if (mapto == mdp -> top)
	    {
	      mdp -> top = moveto;
	      result = (PTR) mdp -> breakval;
	      mdp -> breakval += size;
	    }
	}
      else
	{
	  result = (PTR) mdp -> breakval;
	  mdp -> breakval += size;
	}
    }
  return (result);
}

PTR
__mmalloc_remap_core (mdp)
  struct mdesc *mdp;
{
  caddr_t base;

  /* FIXME:  Quick hack, needs error checking and other attention. */

  base = mmap (mdp -> base, mdp -> top - mdp -> base,
	       PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED,
	       mdp -> fd, 0);
  return ((PTR) base);
}

#else	/* defined(HAVE_MMAP) */
/* Prevent "empty translation unit" warnings from the idiots at X3J11. */
static char ansi_c_idiots = 69;
#endif	/* defined(HAVE_MMAP) */