experiment2.c

   1 #include <sys/types.h>
   2 #include <sys/stat.h>
   3 #include <fcntl.h>
   4 #include <sys/file.h>
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7
   8 int main() {
   9     char filemac[13];
  10     unsigned long int mac;
  11     int fd = open("/mnt/netapp/maccounter", O_RDWR|O_CREAT|O_TRUNC);
  12     flock(fd, LOCK_EX);
  13     FILE * fd2 = fdopen(fd, "r");
  14
  15     if (fd2 == NULL) printf("ga dood\n");
  16     if (fread(filemac, sizeof(char), 13, fd2) == 0) {
  17             printf("read = 0\n");
  18         mac = 0x0;
  19     } else {
  20         mac++;
  21     }
  22
  23     mac = strtoul(filemac, NULL, 16);
  24     printf("cur: %06X\n", mac);
  25     mac++;
  26     snprintf(filemac, 13, "%06X", mac);
  27     printf("next: %s\n", filemac);
  28
  29     lseek(fd, 0, SEEK_SET);
  30     write(fd, &filemac, 13);
  31     close(fd);
  32     flock(fd, LOCK_UN);
  33 }