How to open a file and create all needed directories along the way - http://stackoverflow.com/q/11147850/241521

xopen.c

/* SPDX-License-Identifier: MIT */
/*
 * Copyright (C) 2012 Przemyslaw Pawelczyk <[email protected]>
 *
 * This code is licensed under the terms of the MIT license.
 * https://opensource.org/licenses/MIT
 */

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

/* Look out! It modifies pathname! */
int xopen(char *pathname, int flags, mode_t mode, mode_t dirmode)
{
	int fd, errsv;
	int dirfd = AT_FDCWD;
	char *ptr = pathname;

	while (*ptr == '/')
		ptr++;
	for (;;) {
		strsep(&ptr, "/");
		if (ptr == NULL) {
			fd = openat(dirfd, pathname, flags, mode);
			break;
		}
		while (*ptr == '/')
			ptr++;
		if (*ptr == '\0') {
			errno = EISDIR;
			fd = -1;
			break;
		}
		if ((fd = mkdirat(dirfd, pathname, dirmode)) < 0 && errno != EEXIST)
			break;
		if ((fd = openat(dirfd, pathname, O_DIRECTORY)) < 0)
			break;
		if (dirfd != AT_FDCWD)
			close(dirfd);
		dirfd = fd;
		pathname = ptr;
	}
	errsv = errno;
	if (dirfd != AT_FDCWD)
		close(dirfd);
	errno = errsv;

	return fd;
}

commit d86957660f53549bf8157596a176048f47f8b38c
Author: Przemyslaw Pawelczyk <[email protected]>
Date:   2018-02-06 15:44:57 +0100

    xopen.c: Add copyright notice and MIT license notice.

commit f8c3bf03dd31de2a38c7ebf1d3e145ca09262126
Author: Przemyslaw Pawelczyk <[email protected]>
Date:   2018-02-06 15:48:34 +0100

    Add SPDX License Identifier to all source files.

    The Software Package Data Exchange (SPDX) is a good initiative, it has
    matured over time and deserves accelerated adoption in open-source.

    https://spdx.org/learn
    https://spdx.org/using-spdx
    https://spdx.org/license-list