Read farbfeld image into struct

ff1.c

#include <err.h>
#include <inttypes.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

struct __attribute__((__packed__)) ff_img_s {
    unsigned char magic[8];
    uint32_t width;
    uint32_t height;
    unsigned char data[];
};

int
main(int argc, char **argv)
{
    struct stat s;
    struct ff_img_s *img;
    FILE *f;

    if (argc != 2)
        errx(EXIT_FAILURE, "Usage: ff <file>");
    if (stat(argv[1], &s) != 0)
        err(EXIT_FAILURE, "Cannot stat %s", argv[1]);
    if (s.st_size < 16)
        errx(EXIT_FAILURE, "%s is too small", argv[1]);
    if ((img = malloc(s.st_size)) == NULL)
        err(EXIT_FAILURE, "Cannot allocate memory for reading %s", argv[1]);
    if ((f = fopen(argv[1], "r")) == NULL)
        err(EXIT_FAILURE, "Cannot open %s", argv[1]);
    if (fread(img, 1, s.st_size, f) != (size_t)s.st_size)
        err(EXIT_FAILURE, "Cannot read %s", argv[1]);
    if (fclose(f) != 0)
        err(EXIT_FAILURE, "Cannot close %s", argv[1]);
    if (memcmp(img->magic, "farbfeld", sizeof("farbfeld") - 1) != 0)
        errx(EXIT_FAILURE, "%s is not a farbfeld image", argv[1]);

    (void)printf("W: %"PRIu32"\n", ntohl(img->width));
    (void)printf("H: %"PRIu32"\n", ntohl(img->height));

    free(img);
    return 0;
}