mfdtruncate.c

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#define _GNU_SOURCE   1      /* See feature_test_macros(7) */
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>
#include <stdbool.h>

#define MBSIZE(x) ((x) * 1024 * 1024)

int
main(int argc, char **argv)
{
	int flags = MAP_NORESERVE;
	void *memaddr;
	pid_t pid = getpid();
	char *localmem;
	int fd = memfd_create("mmap_fd_exp", 0);

	size_t size = MBSIZE(300);
	localmem = malloc(size);
	memset(localmem, 1, size);
	if (fd < 0)
	{
		printf("memfd_create failed with errno %d\n", errno);
		exit(__LINE__);
	}
	if (ftruncate(fd, size) < 0)
	{
		printf("ftruncate failed with errno %d on fd = %d and size = %ld\n", errno, fd, size);
		exit(__LINE__);
	}

	memaddr = mmap(NULL, size, PROT_WRITE | PROT_READ, MAP_SHARED | MAP_NORESERVE, fd, 0);
	if (memaddr == MAP_FAILED)
	{
		printf("mmap failed with error %m\n");
		exit(__LINE__);
	}
    memset(memaddr, 1, size);
	if (memcmp(memaddr, localmem, size) != 0)
	{
		printf("mmap memory and local memory are not equal upto size = %ld\n", size);
		exit(__LINE__);
	}
	
    /* causes a segmentation fault: memset(memaddr, 0, maxsize + 1); */
	size = MBSIZE(100);
	if (ftruncate(fd, size) < 0)
	{
		printf("ftruncate failed with errno %d on fd = %d and size = %ld\n", errno, fd, size);
		exit(__LINE__);
	}

    memset(memaddr, 1, size);
	if (memcmp(memaddr, localmem, size) != 0)
	{
		printf("mmap memory and local memory are not equal upto size = %ld\n", size);
		exit(__LINE__);
	}
    /* causes a segmentation fault: memset(memaddr, 1, MBSIZE(200)); */

	size = MBSIZE(200);
	if (ftruncate(fd, size) < 0)
	{
		printf("ftruncate failed with errno %d on fd = %d and size = %ld\n", errno, fd, size);
		exit(__LINE__);
	}

    memset(memaddr, 1, size);
	if (memcmp(memaddr, localmem, size) != 0)
	{
		printf("mmap memory and local memory are not equal upto size = %ld\n", size);
		exit(__LINE__);
	}
}