musl/src/ipc/ftok.c

#include <sys/ipc.h>
#include <sys/stat.h>

key_t ftok(const char *path, int id)
{
	struct stat st;
	if (stat(path, &st) < 0) return -1;

	return ((st.st_ino & 0xffff) | ((st.st_dev & 0xff) << 16) | ((id & 0xff) << 24));
}