#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>

#include <cuda.h>
#include <cuda_runtime.h>

char *getTime()
{
   time_t now = time(NULL);
   char *result = ctime(&now);
   result[strlen(result) - 1] = '\0';
   return result;
}

int main(int argc, char **argv)
{
   // fork a new process
   pid_t cpid = fork();
   if (cpid < 0) 
      {
      printf("ERROR: fork() not successful\n");
      exit(EXIT_FAILURE);
      }

   // exit the parent process
   if (cpid > 0) exit(0);

   // unmask the file mode
   umask(0);

   // create a new session for the daemon process
   pid_t sid = setsid();
   if (sid < 0)
      {
      printf("ERROR: setsid() not successful\n");
      exit(EXIT_FAILURE);
      }

   // change directory to root
   chdir("/");

   // close all file handles
   close(STDIN_FILENO);
   close(STDOUT_FILENO);
   close(STDERR_FILENO);

   // create log file
   FILE *fp = fopen("/tmp/cuda_lock_driver.log", "w");
   fprintf(fp, "%s - INFO: cuda_lock_driver started\n", getTime());
   fclose(fp);

   // start CUDA device locking
   int deviceCountOld = -1;

   while (true)
      {
      int deviceCount = 0;
      cudaError_t error_id = cudaGetDeviceCount(&deviceCount);
      if (error_id != cudaSuccess)
         {
         FILE *fp = fopen("/tmp/cuda_lock_driver.log", "a");
         fprintf(fp, "%s - ERROR: cudaGetDeviceCount() returned %d\n-> %s\n", getTime(), (int)error_id, cudaGetErrorString(error_id));
         fclose(fp);
         exit(EXIT_FAILURE);
         }

      if (deviceCountOld == -1) deviceCountOld = deviceCount;

      FILE *fp = fopen("/tmp/cuda_lock_driver.log", "a");
      fprintf(fp, "%s - INFO: cudaGetDeviceCount() returned %d\n", getTime(), deviceCount);
      fclose(fp);

      if (deviceCountOld != deviceCount)
         {
         FILE *fp = fopen("/tmp/cuda_lock_driver.log", "a");
         printf("%s - ERROR: cudaGetDeviceCount() result has changed from %d to %d\n", getTime(), deviceCountOld, deviceCount);
         fclose(fp);
         exit(EXIT_FAILURE);
         }

      sleep(15 * 60);
      }
}