diropen.h

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#ifndef DIROPEN_H
#define DIROPEN_H

#define _GNU_SOURCE /* needed for O_PATH according to manpage */
#define __USE_GNU /* needed for O_PATH according to code */
#include <fcntl.h>
#undef __USE_GNU /* seems to cause chaos if visible at other places */
#include <unistd.h>
#include <sys/stat.h>

#if O_DIRECTORY == 0
#include <errno.h>
#include <sys/stat.h>
#endif /* O_DIRECTORY == 0 */

static inline int __attribute__ ((nonnull (2)))
get_dirfd(int base, const char *dirname)
{
        int fd;

#ifdef O_PATH /* recent Linux */
        fd = openat(base, dirname, O_PATH | O_DIRECTORY | O_CLOEXEC);
#elif defined(O_SEARCH)
        fd = openat(base, dirname, O_SEARCH | O_DIRECTORY | O_CLOEXEC);
#else /* O_SEARCH */
        fd = openat(base, dirname, O_RDONLY | O_DIRECTORY | O_CLOEXEC);
#endif /* O_PATH */

#if O_DIRECTORY == 0
        {
        struct stat st;
        /* in case O_DIRECTORY is not supported make sure that this really is
         * a directory */
        if (fstat(fd, &st) != 0) {
                int e = errno;
                close(fd);
                errno = e;
                return -1;
        }

        if (!S_ISDIR(st.st_mode)) {
                close(fd);
                errno = ENOTDIR;
                return -1;
        }
        }
#endif /* O_DIRECTORY */

        return fd;
}

#endif /* DIROPEN_H */