show sparse file map

sparsemap.c

#define _FILE_OFFSET_BITS 64
#define _GNU_SOURCE 1

#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

#ifndef SEEK_DATA
#warning "SEEK_DATA is undeclared and manually defined."
#define SEEK_DATA 3 /* seek to the next data */
#endif
#ifndef SEEK_HOLE
#warning "SEEK_HOLE is undeclared and manually defined."
#define SEEK_HOLE 4 /* seek to the next hole */
#endif


int main(int argc, char ** argv)
{
    if (argc != 2) {
        fprintf(stderr, "Usage: %s file\n", argv[0]);
    }

    int fd = open(argv[1], O_RDONLY);
    if(fd == -1) {
        perror("failed to open the file.");
        exit(EXIT_FAILURE);
    }

    off_t offset = 0;
    struct stat status;
    fstat(fd, &status);
    const off_t size = status.st_size;

    do {
        off_t data = lseek(fd, offset, SEEK_DATA);
        off_t hole = lseek(fd, offset, SEEK_HOLE);

        if (data == -1 && hole == -1) {
            data = offset;
        }

        if (data == offset) {
            if (hole == -1) {
                hole = size;
            }
            fprintf(stdout, "data: %lld %lld\n",
                (unsigned long long)data,
                (unsigned long long)hole);
        }

        if (hole == offset) {
            if (data == -1) {
                data = size;
            }
            fprintf(stdout, "hole: %lld %lld\n",
                (unsigned long long)hole,
                (unsigned long long)data);
        }

        offset = MAX(data, hole);
    } while (offset < size);

    return 0;
}