git.scottworley.com Git - overonion/blob - reverse_lib.c

   1 #define _FILE_OFFSET_BITS 64
   2
   3 #include <err.h>
   4 #include <fcntl.h>
   5 #include <stdio.h>
   6 #include <sys/mman.h>
   7 #include <sys/stat.h>
   8 #include <sys/types.h>
   9 #include <sysexits.h>
  10 #include <unistd.h>
  11
  12 void reverse_file(const char* input_filename, FILE* output_stream) {
  13   int fd = open(input_filename, O_RDONLY);
  14   if (fd == -1) err(EX_NOINPUT, "Could not open specified file");
  15
  16   struct stat stats;
  17   if (fstat(fd, &stats) == -1) err(EX_NOINPUT, "Could not stat input");
  18
  19   long page_size = sysconf(_SC_PAGE_SIZE);
  20   off_t pages = (stats.st_size - 1) / page_size + 1;
  21   long map_size = pages * page_size;
  22   char *m = mmap(NULL, map_size, PROT_READ, MAP_SHARED, fd, 0);
  23   if (m == MAP_FAILED) err(EX_NOINPUT, "Could not mmap input");
  24
  25   for (off_t p = stats.st_size - 1; p >= 0; p--) {
  26     if (fputc(m[p], output_stream) == EOF) errx(EX_IOERR, "Could not write");
  27   }
  28
  29   if (munmap(m, map_size) == -1) err(EX_IOERR, "Could not unmap input");
  30   if (close(fd) == -1) err(EX_IOERR, "Could not close input");
  31 }