osdep/mmap_anon.c

   1 /*
   2  * This file is part of MPlayer.
   3  *
   4  * MPlayer is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * MPlayer is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License along
  15  * with MPlayer; if not, write to the Free Software Foundation, Inc.,
  16  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  17  */
  18
  19  /**
  20  * \file mmap_anon.c
  21  * \brief Provide a compatible anonymous space mapping function
  22  */
  23 #include "config.h"
  24
  25 #include <stdio.h>
  26 #include <unistd.h>
  27 #include <fcntl.h>
  28 #include <sys/mman.h>
  29
  30 #include "mmap_anon.h"
  31
  32 #if defined(MAP_ANON) && !defined(MAP_ANONYMOUS)
  33 #define MAP_ANONYMOUS MAP_ANON
  34 #endif
  35
  36 /*
  37  * mmap() anonymous space, depending on the system's mmap() style. On systems
  38  * that use the /dev/zero mapping idiom, zerofd will be set to the file descriptor
  39  * of the opened /dev/zero.
  40  */
  41
  42  /**
  43  * \brief mmap() anonymous space, depending on the system's mmap() style. On systems
  44  * that use the /dev/zero mapping idiom, zerofd will be set to the file descriptor
  45  * of the opened /dev/zero.
  46  *
  47  * \param addr address to map at.
  48  * \param len number of bytes from addr to be mapped.
  49  * \param prot protections (region accessibility).
  50  * \param flags specifies the type of the mapped object.
  51  * \param offset start mapping at byte offset.
  52  * \param zerofd
  53  * \return a pointer to the mapped region upon successful completion, -1 otherwise.
  54  */
  55 void *mmap_anon(void *addr, size_t len, int prot, int flags, off_t offset)
  56 {
  57     void *result;
  58
  59      /* From loader/ext.c:
  60       * "Linux EINVAL's on us if we don't pass MAP_PRIVATE to an anon mmap"
  61       * Therefore we preserve the same behavior on all platforms, ie. no
  62       * shared mappings of anon space (if the concepts are supported). */
  63 #if defined(MAP_SHARED) && defined(MAP_PRIVATE)
  64      flags = (flags & ~MAP_SHARED) | MAP_PRIVATE;
  65 #endif /* defined(MAP_SHARED) && defined(MAP_PRIVATE) */
  66
  67 #ifdef MAP_ANONYMOUS
  68     /* BSD-style anonymous mapping */
  69     result = mmap(addr, len, prot, flags | MAP_ANONYMOUS, -1, offset);
  70 #else
  71     /* SysV-style anonymous mapping */
  72     int fd;
  73     fd = open("/dev/zero", O_RDWR);
  74     if(fd < 0){
  75         perror( "Cannot open /dev/zero for READ+WRITE. Check permissions! error: ");
  76         return NULL;
  77     }
  78
  79     result = mmap(addr, len, prot, flags, fd, offset);
  80     close(fd);
  81 #endif /* MAP_ANONYMOUS */
  82
  83     return result;
  84 }