List directories using getdents()

gs.c

/*
 * List directories using getdents() because ls, find and Python libraries
 * use readdir() which is slower (but uses getdents() underneath.
 *
 * $ gcc  gs.c -o gs
*/

#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <string.h>
#include <limits.h>

#define handle_error(msg) \
       do { perror(msg); exit(EXIT_FAILURE); } while (0)

struct linux_dirent {
   long           d_ino;
   off_t          d_off;
   unsigned short d_reclen;
   char           d_name[];
};

#define BUF_SIZE 1024*1024*5

void apply_color(mode_t mode, char *name) {
    if (S_ISDIR(mode)) {
        printf("\033[1;34m%s\033[0m", name); // Blue for directories
    } else if (S_ISLNK(mode)) {
        printf("\033[1;36m%s\033[0m", name); // Cyan for symlinks
    } else if (mode & S_IXUSR) {
        printf("\033[1;32m%s\033[0m", name); // Green for executables
    } else {
        printf("%s", name); // Default color
    }
}

void list_directory(const char *path, int show_hidden) {
    int fd, nread;
    char buf[BUF_SIZE];
    struct linux_dirent *d;
    int bpos;
    char d_type;
    struct stat st;
    char fullpath[PATH_MAX];

    fd = open(path, O_RDONLY | O_DIRECTORY);
    if (fd == -1)
        handle_error("open");

    for (;;) {
        nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
        if (nread == -1)
            handle_error("getdents");

        if (nread == 0)
            break;

        for (bpos = 0; bpos < nread;) {
            d = (struct linux_dirent *) (buf + bpos);
            d_type = *(buf + bpos + d->d_reclen - 1);

            // Skip "." and ".."
            if (strcmp(d->d_name, ".") == 0 || strcmp(d->d_name, "..") == 0) {
                bpos += d->d_reclen;
                continue;
            }

            // Skip hidden files unless `-a` is provided
            if (!show_hidden && d->d_name[0] == '.') {
                bpos += d->d_reclen;
                continue;
            }

            snprintf(fullpath, sizeof(fullpath), "%s/%s", path, d->d_name);

            if (stat(fullpath, &st) == -1) {
                perror("stat");
                bpos += d->d_reclen;
                continue;
            }

            apply_color(st.st_mode, d->d_name);
            printf("\n");
            bpos += d->d_reclen;
        }
    }

    close(fd);
}

int main(int argc, char *argv[]) {
    int show_hidden = 0;
    char *path = ".";

    for (int i = 1; i < argc; i++) {
        if (strcmp(argv[i], "-a") == 0) {
            show_hidden = 1;
        } else {
            path = argv[i];
        }
    }

    list_directory(path, show_hidden);
    return 0;
}