diff --git a/include/linux/projid.h b/include/linux/projid.h
new file mode 100644
index 0000000..36517b9
--- /dev/null
+++ b/include/linux/projid.h
@@ -0,0 +1,104 @@
+#ifndef _LINUX_PROJID_H
+#define _LINUX_PROJID_H
+
+/*
+ * A set of types for the internal kernel types representing project ids.
+ *
+ * The types defined in this header allow distinguishing which project ids in
+ * the kernel are values used by userspace and which project id values are
+ * the internal kernel values.  With the addition of user namespaces the values
+ * can be different.  Using the type system makes it possible for the compiler
+ * to detect when we overlook these differences.
+ *
+ */
+#include <linux/types.h>
+
+struct user_namespace;
+extern struct user_namespace init_user_ns;
+
+typedef __kernel_uid32_t projid_t;
+
+#ifdef CONFIG_UIDGID_STRICT_TYPE_CHECKS
+
+typedef struct {
+	projid_t val;
+} kprojid_t;
+
+static inline projid_t __kprojid_val(kprojid_t projid)
+{
+	return projid.val;
+}
+
+#define KPROJIDT_INIT(value) (kprojid_t){ value }
+
+#else
+
+typedef projid_t kprojid_t;
+
+static inline projid_t __kprojid_val(kprojid_t projid)
+{
+	return projid;
+}
+
+#define KPROJIDT_INIT(value) ((kprojid_t) value )
+
+#endif
+
+#define INVALID_PROJID KPROJIDT_INIT(-1)
+#define OVERFLOW_PROJID 65534
+
+static inline bool projid_eq(kprojid_t left, kprojid_t right)
+{
+	return __kprojid_val(left) == __kprojid_val(right);
+}
+
+static inline bool projid_lt(kprojid_t left, kprojid_t right)
+{
+	return __kprojid_val(left) < __kprojid_val(right);
+}
+
+static inline bool projid_valid(kprojid_t projid)
+{
+	return !projid_eq(projid, INVALID_PROJID);
+}
+
+#ifdef CONFIG_USER_NS
+
+extern kprojid_t make_kprojid(struct user_namespace *from, projid_t projid);
+
+extern projid_t from_kprojid(struct user_namespace *to, kprojid_t projid);
+extern projid_t from_kprojid_munged(struct user_namespace *to, kprojid_t projid);
+
+static inline bool kprojid_has_mapping(struct user_namespace *ns, kprojid_t projid)
+{
+	return from_kprojid(ns, projid) != (projid_t)-1;
+}
+
+#else
+
+static inline kprojid_t make_kprojid(struct user_namespace *from, projid_t projid)
+{
+	return KPROJIDT_INIT(projid);
+}
+
+static inline projid_t from_kprojid(struct user_namespace *to, kprojid_t kprojid)
+{
+	return __kprojid_val(kprojid);
+}
+
+static inline projid_t from_kprojid_munged(struct user_namespace *to, kprojid_t kprojid)
+{
+	projid_t projid = from_kprojid(to, kprojid);
+	if (projid == (projid_t)-1)
+		projid = OVERFLOW_PROJID;
+	return projid;
+}
+
+static inline bool kprojid_has_mapping(struct user_namespace *ns, kprojid_t projid)
+{
+	return true;
+}
+
+#endif /* CONFIG_USER_NS */
+
+#endif /* _LINUX_PROJID_H */