demo for using memfd_create() to shared raw memory between processes

test_memfd_create.cpp

//#include <sys/memfd.h>
#include <sys/syscall.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
} while (0)

int main(int argc, char *argv[])
{
  int fd;
  char *name;
  ssize_t i, len;
  unsigned char* addr;
  struct stat st;

  if (argc < 3) {
    fprintf(stderr, "%s name size\n", argv[0]);
    exit(EXIT_FAILURE);
  }

  name = argv[1];
  len = atoi(argv[2]) * 1024LU * 1024LU * 1024LU;

  /* Create an anonymous file in tmpfs; */

  fd = syscall (SYS_memfd_create, name, 0);

  if (fd == -1)
    errExit("memfd_create");

  /* Size the file as specified on the command line */

  printf("length: %zu\n", len);
  if (ftruncate(fd, len) == -1)
    errExit("truncate");

  if (fstat (fd, &st))
    errExit ("fstat");

  printf("PID: %ld; fd: %d; /proc/%ld/fd/%d, atime: %lu.%lu\n",
      (long) getpid(), fd, (long) getpid(), fd, st.st_atim.tv_sec, st.st_atim.tv_nsec);

  addr = (unsigned char*) mmap (NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  if (addr == MAP_FAILED)
    errExit("mmap");

  for (i = 0; i < len; ++i)
    addr[i] = i & 0x000000FF;

  if (fstat (fd, &st))
    errExit ("fstat");

  printf("length: %zu, atime: %lu.%lu\n", len, st.st_atim.tv_sec, st.st_atim.tv_nsec);

  /* Keep running, so that the file created by memfd_create()
     continues to exist */


  sleep (60);

  printf("length: %zu, atime: %lu.%lu\n", len, st.st_atim.tv_sec, st.st_atim.tv_nsec);

  exit(EXIT_SUCCESS);
}

test_memfd_open.cpp

#include <sys/syscall.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
} while (0)

int main(int argc, char *argv[])
{
  int fd;
  char *name;
  ssize_t i, len;
  unsigned char* addr;
  struct stat st;

  if (argc != 2) {
    fprintf(stderr, "%s /proc/PID/fd/FD\n", argv[0]);
    exit(EXIT_FAILURE);
  }

  fd = open(argv[1], O_RDWR);
  if (fd == -1)
    errExit("open");

  if (fstat (fd, &st))
    errExit ("fstat");


  name = argv[1];
  len = st.st_size;

  printf("length: %zu, atime: %lu.%lu\n", len, st.st_atim.tv_sec, st.st_atim.tv_nsec);

  addr = (unsigned char*) mmap (NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  if (addr == MAP_FAILED)
    errExit("mmap");

  printf ("start: ");
  for (i = 0; i < 32; ++i)
    printf ("%i ", addr[i]);
  printf ("\nend: ");
  for (i = 0; i < 32; ++i)
    printf ("%i ", addr[len-32+i]);
  printf ("\ndone\n");

  pause();

  exit(EXIT_SUCCESS);
}