List contents of extremely large directories

listdir.c

#define _GNU_SOURCE
#include <dirent.h>     /* Defines DT_* constants */
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/syscall.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 * 10

int
main(int argc, char *argv[])
{
	int fd, nread;
	char buf[BUF_SIZE];
	struct linux_dirent *d;
	int bpos;
	char d_type;

	fd = open(argc > 1 ? argv[1] : ".", 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;

#if 0
		printf("--------------- nread=%d ---------------\n", nread);
		printf("i-node#  file type  d_reclen  d_off   d_name\n");
#endif

		for (bpos = 0; bpos < nread;) {
			d = (struct linux_dirent *) (buf + bpos);
			if (d->d_ino == 0) continue;

#if 0
			printf("%8ld  ", d->d_ino);
			d_type = *(buf + bpos + d->d_reclen - 1);
			printf("%-10s ", (d_type == DT_REG) ?  "regular" :
					(d_type == DT_DIR) ?  "directory" :
					(d_type == DT_FIFO) ? "FIFO" :
					(d_type == DT_SOCK) ? "socket" :
					(d_type == DT_LNK) ?  "symlink" :
					(d_type == DT_BLK) ?  "block dev" :
					(d_type == DT_CHR) ?  "char dev" : "???");
			printf("%4d %10lld  %s\n", d->d_reclen,
					(long long) d->d_off, (char *) d->d_name);
#endif
			printf("%s\n", d->d_name);
			bpos += d->d_reclen;
		}
	}

	exit(EXIT_SUCCESS);
}