/*
 * Close all open file descriptors.
 */
#include <stdlib.h>
#include <stdio.h>
#include <stddef.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <dirent.h>
#include <errno.h>

const char dirpath[] = "/proc/self/fd";

static void close_fds_linux() {
	printf("close_fds_linux()\n");

	DIR *dirp = opendir(dirpath);
	if (!dirp)
		perror("opendir()");

	long name_max = fpathconf(dirfd(dirp), _PC_NAME_MAX);
	if (name_max == -1)	/* Limit not defined, or error */
		name_max = 255;	/* Take a guess */
	size_t len = offsetof(struct dirent, d_name) + name_max + 1;

	struct dirent *result, *entryp = malloc(len);
	if (!entryp)
		perror("malloc()");

	for (;;) {
		int ret = readdir_r(dirp, entryp, &result);
		if (ret)
			perror("readdir_r()");
		if (!result)
			break;
		switch (result->d_name[0]) {
			case '0': /* STDIN */
			case '1': /* STDOUT */
			case '2': /* STDERR */
				if (result->d_name[1] != '\0')
					break;
				/* fall-through */
			case '.':
				continue;
		}
		int fd = atoi(result->d_name);
		if (fd == dirfd(dirp))
			continue;
		printf("Closing %d...\n", fd);
		ret = close(fd);
		if (ret)
			perror("close()");
	}

	free(entryp);

	int ret = closedir(dirp);
	if (ret)
		perror("closedir()");
}

static void close_fds_generic() {
	printf("close_fds_generic()\n");

	int fd = sysconf(_SC_OPEN_MAX);
	if (fd < 0)
		perror("sysconf()");
	while (fd > STDERR_FILENO) {
		printf("Closing %d...\n", fd);
		int ret = close(fd--);
		if (ret && errno != EBADF)
			perror("close()");
	}
}

static void close_fds() {
	struct stat buf;
	int ret = stat(dirpath, &buf);
	if (!ret && S_ISDIR(buf.st_mode))
		close_fds_linux();
	else if (ret && errno == ENOENT)
		close_fds_generic();
	else
		perror("stat()");
}

int main(void) {
	close_fds();
	return 0;
}