#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <unistd.h>

int main()
{
    const char   *filePath     = "/mnt/ram0/tests_mmap_fallocate";
    const size_t fileSize      = 50 << 20;
    const int   fileFlags      = O_RDWR | O_CREAT | O_EXCL;
    int         fileDescriptor = open(filePath, fileFlags, 0644);

    if (fileDescriptor == -1)
    {
        perror("Cannot open file");
        exit(1);
    }

    char *buffer = mmap(NULL, fileSize, PROT_READ | PROT_WRITE, MAP_SHARED, fileDescriptor, 0);
    if (buffer == MAP_FAILED)
    {
        perror("Cannot memory map");
        exit(1);
    }

    for (size_t i = 0; i < fileSize; i++)
    {
        if (fallocate(fileDescriptor, 0, i, 1) != 0)
        {
            perror("Cannot fallocate");
            exit(1);
        }

        buffer[i] = 10;

        if (buffer[i] != 10)
        {
            fprintf(stderr, "Value not written correctly\n");
            exit(1);
        }
    }

    for (size_t i = 0; i < fileSize; i++)
    {
        if (buffer[i] != 10)
        {
            fprintf(stderr, "Value has been modified\n");
            exit(1);
        }
    }

    munmap(buffer, fileSize);
    close(fileDescriptor);

    return 0;
}