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 #if defined(MAP_ANON) && !defined(MAP_ANONYMOUS)
  31 #define MAP_ANONYMOUS MAP_ANON
  32 #endif
  33
  34 /*
  35  * mmap() anonymous space, depending on the system's mmap() style. On systems
  36  * that use the /dev/zero mapping idiom, zerofd will be set to the file descriptor
  37  * of the opened /dev/zero.
  38  */
  39
  40  /**
  41  * \brief mmap() anonymous space, depending on the system's mmap() style. On systems
  42  * that use the /dev/zero mapping idiom, zerofd will be set to the file descriptor
  43  * of the opened /dev/zero.
  44  *
  45  * \param addr address to map at.
  46  * \param len number of bytes from addr to be mapped.
  47  * \param prot protections (region accessibility).
  48  * \param flags specifies the type of the mapped object.
  49  * \param offset start mapping at byte offset.
  50  * \param zerofd
  51  * \return a pointer to the mapped region upon successful completion, -1 otherwise.
  52  */
  53 void *mmap_anon(void *addr, size_t len, int prot, int flags, off_t offset)
  54 {
  55     void *result;
  56
  57      /* From loader/ext.c:
  58       * "Linux EINVAL's on us if we don't pass MAP_PRIVATE to an anon mmap"
  59       * Therefore we preserve the same behavior on all platforms, ie. no
  60       * shared mappings of anon space (if the concepts are supported). */
  61 #if defined(MAP_SHARED) && defined(MAP_PRIVATE)
  62      flags = (flags & ~MAP_SHARED) | MAP_PRIVATE;
  63 #endif /* defined(MAP_SHARED) && defined(MAP_PRIVATE) */
  64
  65 #ifdef MAP_ANONYMOUS
  66     /* BSD-style anonymous mapping */
  67     result = mmap(addr, len, prot, flags | MAP_ANONYMOUS, -1, offset);
  68 #else
  69     /* SysV-style anonymous mapping */
  70     int fd;
  71     fd = open("/dev/zero", O_RDWR);
  72     if(fd < 0){
  73         perror( "Cannot open /dev/zero for READ+WRITE. Check permissions! error: ");
  74         return NULL;
  75     }
  76
  77     result = mmap(addr, len, prot, flags, fd, offset);
  78     close(fd);
  79 #endif /* MAP_ANONYMOUS */
  80
  81     return result;
  82 }