metafile.c

#define _XOPEN_SOURCE 700
#include <stdlib.h>
#include <unistd.h>
#include <ftw.h>
#include <stdio.h>
#include <string.h>
#include <sys/sysmacros.h>

char typechar(int typeflag)
{
    switch(typeflag & S_IFMT) {
        case S_IFLNK:
            return 's';
        case S_IFREG:
            return 'f';
        case S_IFDIR:
            return 'd';
        case S_IFCHR:
            return 'c';
        default:
            return '?';
    }
}

int nlinks = 0;
ino_t* links = NULL;
char** files = NULL;

int print_entry(const char *filepath, const struct stat *info,
                const int typeflag, struct FTW *pathinfo)
{
    const char *const filename = filepath + pathinfo->base;

    char type = typechar(info->st_mode);
    char* link = NULL;
    // Check for duplicate hardlinks
    if(type == 'f' && info->st_nlink > 1) {
        // Search for links to see if we find a matching one
        for(int i=0;i<nlinks;i++) {
            if(info->st_ino == links[i]) {
                // Found a matching hardlink
                type = 'h';
                // Overwrite link with the filename that we are pointing to
                link=files[i];
                break;
            }
        }
        if(type != 'h') {
            // This is the first instance of this inode, we must add it
            links = realloc(links, sizeof(ino_t) * (nlinks+1));
            files = realloc(files, sizeof(char*) * (nlinks+1));
            links[nlinks] = info->st_ino;
            files[nlinks] = malloc(strlen(filepath) + 1);
            strcpy(files[nlinks], filepath);
            nlinks++;
        }
    }
    if(type == 's') {
        // Resolve symlink
        link = malloc(1024);
        ssize_t length = readlink(filepath, link, 1023);
        link[length] = 0; // Manually null-terminate string
    }
    printf("%s\t%06o\t%d\t%d\t%c\t", filepath, info->st_mode, info->st_uid, info->st_gid, type);
    if(type == 'c') {
        printf("%d,%d\n",major(info->st_rdev),minor(info->st_rdev));
    } else if(link == NULL) {
        printf("\n");
    } else {
        printf("%s\n", link);
    }
    if(type == 's') {
        free(link);
    }

    return 0;
}

int main(int argc, char *argv[])
{
    printf("#<file>\t<permissions>\t<owner>\t<group>\t<type>\t<extra>\n");
    // https://stackoverflow.com/a/29402705 saved my life from programming this manually
    return nftw(".", print_entry, 15, FTW_PHYS);
}