trivial example showing how to use opendir+openat

opendir_and_openat.c

/*
 * opendir_and_openat.c -- trivial example showing how to use opendir+openat
 *
 * usage: a.out path-to-directory
 */

#include <stdio.h>
#include <dirent.h>
#include <err.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
	if (argc != 2) {
		fprintf(stderr, "usage: %s dirname\n", argv[0]);
		exit(1);
	}

	int dfd = open(argv[1], O_RDONLY);

	if (dfd < 0)
		err(1, argv[1]);

	DIR *dirp = fdopendir(dfd);

	if (dirp == NULL)
		err(1, "opendir: %s", argv[1]);

	struct dirent *dp;

	while ((dp = readdir(dirp)) != NULL) {
		if ((strcmp(dp->d_name, ".") == 0) ||
				(strcmp(dp->d_name, "..") == 0))
			continue;

		struct stat stbuf;
		int fd = openat(dfd, dp->d_name, O_RDONLY);

		if (fd < 0 || fstat(fd, &stbuf) < 0) {
			warn("skipping %s/%s", argv[1], dp->d_name);
			continue;
		}

		if (!S_ISREG(stbuf.st_mode)) {
			warnx("%s: not a regular file", dp->d_name);
			continue;
		}

		printf("processing file \"%s\"\n", dp->d_name);

		close(fd);
	}

	closedir(dirp);

	printf("done.\n");
	exit(0);
}