diff --git a/cmds/idmap/idmap.h b/cmds/idmap/idmap.h
new file mode 100644
index 0000000..f507dd8
--- /dev/null
+++ b/cmds/idmap/idmap.h
@@ -0,0 +1,34 @@
+#ifndef _IDMAP_H_
+#define _IDMAP_H_
+
+#define LOG_TAG "idmap"
+
+#include <utils/Log.h>
+
+#include <errno.h>
+#include <stdio.h>
+
+#ifndef TEMP_FAILURE_RETRY
+// Used to retry syscalls that can return EINTR.
+#define TEMP_FAILURE_RETRY(exp) ({         \
+    typeof (exp) _rc;                      \
+    do {                                   \
+        _rc = (exp);                       \
+    } while (_rc == -1 && errno == EINTR); \
+    _rc; })
+#endif
+
+int idmap_create_path(const char *target_apk_path, const char *overlay_apk_path,
+        const char *idmap_path);
+
+int idmap_create_fd(const char *target_apk_path, const char *overlay_apk_path, int fd);
+
+// Regarding target_package_name: the idmap_scan implementation should
+// be able to extract this from the manifest in target_apk_path,
+// simplifying the external API.
+int idmap_scan(const char *overlay_dir, const char *target_package_name,
+        const char *target_apk_path, const char *idmap_dir);
+
+int idmap_inspect(const char *idmap_path);
+
+#endif // _IDMAP_H_