testing memory mapped files

memory-mapped-test.c

#include <stdio.h>
#include <errno.h>
#include <stdint.h>

#ifdef _WIN32
#include <windows.h>
#include <io.h>
#else
#include <sys/mman.h>
#endif

int unmap_file(uint8_t *map, uint64_t filesize)
{
#ifdef _WIN32
    if (!FlushViewOfFile(map, filesize)) {
        return GetLastError();
    }
    if (!UnmapViewOfFile(map)) {
        return GetLastError();
    }
#else
    if (munmap(map, filesize)) {
       return errno;
    }

#endif
    return 0;
}

int map_file(int fd, uint64_t filesize, uint8_t **map)
{
    int status = 0;
#ifdef _WIN32
    HANDLE fh = (HANDLE)_get_osfhandle(fd);
    if (fh == INVALID_HANDLE_VALUE) {
        return EBADF;
    }

    HANDLE mh = CreateFileMapping(fh, NULL, PAGE_READWRITE, 0, 0, NULL);
    if (!mh) {
        status = GetLastError();
        goto win_finished;
    }

    *map = MapViewOfFileEx(mh, FILE_MAP_WRITE, 0, 0, filesize, NULL);
    if (!*map) {
        status = GetLastError();
        goto win_finished;
    }

win_finished:
    CloseHandle(mh);
    CloseHandle(fh);
    return status;

#else
    *map = (uint8_t *)mmap(NULL, filesize, PROT_READ, MAP_SHARED, fd, 0);
    if (*map == MAP_FAILED) {
        status = errno;
    }
    return status;
#endif
}


int main()
{
    FILE *fp = fopen("video.ogv", "r+");
    int fd = fileno(fp);

    if (!fp) {
        printf("failed open.\n");
        return 1;
    }

    fseek(fp, 0L, SEEK_END);
    uint64_t filesize = ftell(fp);
    rewind(fp);

    printf("filesize: %lu\n", filesize);

    uint8_t *zero = NULL;
    int error = map_file(fd, filesize, &zero);
    if (error) {
        printf("failed w/ code: %d\n", error);
        return error;
    }

    printf("value: %i\n", zero[40001]);

    error = unmap_file(zero, filesize);
    if (error) {
        printf("failed to unmap file: %d", error);
        return error;
    }

}