mmap from man 

   1:  /*
   2:  author:justinzhang
   3:  email:uestczhangchao@gmail.com
   4:  time：2012-8-22 16:23:08
   5:  desc: mmap()practice from man mmap
   6:  */
   7:  #include <sys/mman.h>
   8:  #include <sys/stat.h>
   9:  #include <fcntl.h>
  10:  #include <stdio.h>
  11:  #include <stdlib.h>
  12:  #include <unistd.h>
  13:   
  14:  #define handle_error(msg)\
  15:  do { perror(msg); exit(EXIT_FAILURE); } while(0)
  16:  int 
  17:  main(int argc, char *argv[])
  18:  {
  19:      char *addr;
  20:      int fd;
  21:      struct stat sb;
  22:      off_t offset, pa_offset;
  23:      size_t length;
  24:      ssize_t s;
  25:      if(argc <3 || argc > 4)
  26:      {
  27:          fprintf(stderr, "%s file offset [length]\n",argv[0]);
  28:      exit(EXIT_FAILURE);
  29:      }
  30:      fd = open(argv[1],O_RDONLY);
  31:      if(fd == -1)
  32:      {
  33:          handle_error("open");
  34:      }
  35:      if(fstat(fd, &sb) == -1)/*to obtain file size*/
  36:      {
  37:          handle_error("fstat");
  38:      }
  39:      offset = atoi(argv[2]);
  40:      pa_offset = offset & ~(sysconf(_SC_PAGE_SIZE)-1);
  41:         /*offset for mmap() must be page aligned*/
  42:      if( offset >= sb.st_size)
  43:      {
  44:          fprintf(stderr, "offset is past end of file\n");
  45:      exit(EXIT_FAILURE);
  46:      }
  47:      if(argc == 4)
  48:      {
  49:          length = atoi(argv[3]);
  50:      if(offset + length > sb.st_size)
  51:          length = sb.st_size - offset;
  52:          /*can't display bytes past end of file*/
  53:      }else {/*No length arg ==> display to end of file*/
  54:          length = sb.st_size - offset;
  55:      }
  56:      addr = mmap(NULL, length + offset - pa_offset, PROT_READ,MAP_PRIVATE, fd
  57:                  ,pa_offset);
  58:      if(addr == MAP_FAILED)
  59:          handle_error("mmap");
  60:      s = write(STDOUT_FILENO, addr + offset - pa_offset, length);
  61:      if (s != length)
  62:      {
  63:          if (s == -1)
  64:          handle_error("write");
  65:      fprintf(stderr, "partial write");
  66:      exit(EXIT_FAILURE); 
  67:      }
  68:      exit(EXIT_SUCCESS); 
  69:  }
posted @ 2012-09-01 23:35  justinzhang  阅读(445)  评论(0)  编辑  收藏  举报