o_path.c

/* $Id: o_path.c,v 1.4 2021/03/18 12:01:23 kostik Exp $ */

#include <sys/fcntl.h>
#include <sys/stat.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#ifdef __FreeBSD__
#ifndef O_PATH
#define O_PATH		0x00400000	/* fd is only a path */
#endif
#endif

static void
opath(const char *dirname, const char *filename)
{
	struct stat st;
	int dirfd, fd, error;
	char c[1];

	dirfd = open(dirname, O_PATH | O_RDONLY);
	if (dirfd == -1) {
		fprintf(stderr, "Cannot open(\"%s\", O_PATH): %d %s",
		    dirname, errno, strerror(errno));
		return;
	}

	if (fstat(dirfd, &st) == -1) {
		fprintf(stderr, "Cannot fstat(\"%s\", O_PATH): %d %s",
		    dirname, errno, strerror(errno));
		return;
	}

	error = read(dirfd, c, sizeof(c));
	if (error >= 0) {
		fprintf(stderr, "read dirfd returned %d\n", error);
	} else {
		fprintf(stderr, "read dirfd error %d %s\n",
		    errno, strerror(errno));
	}

	fd = openat(dirfd, filename, O_RDONLY);
	if (fd == -1) {
		fprintf(stderr, "Cannot open(\"%s\"): %d %s",
		    filename, errno, strerror(errno));
		close(dirfd);
		return;
	}

	if (close(dirfd) == -1) {
		fprintf(stderr, "Cannot close(\"%s\"): %d %s",
		    dirname, errno, strerror(errno));
	}

	if (close(fd) == -1) {
		fprintf(stderr, "Cannot close(\"%s\"): %d %s",
		    filename, errno, strerror(errno));
	}
}

int
main(int argc, char *argv[])
{
	for (int i = 1; i < argc; i += 2) {
		opath(argv[i], argv[i + 1]);
	}
}