Add the fsverity API definition

Signed-off-by: Eric Biggers <ebiggers@google.com>
diff --git a/fsverity_api.h b/fsverity_api.h
new file mode 100644
index 0000000..db0483f
--- /dev/null
+++ b/fsverity_api.h
@@ -0,0 +1,44 @@
+#ifndef _FSVERITY_KERNEL_DEFS_H
+#define _FSVERITY_KERNEL_DEFS_H
+
+#include <linux/limits.h>
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+/* file-based verity support */
+
+/*
+ * TODO(ebiggers):  What is the purpose of this structure?  It's not actually
+ * used for anything.
+ */
+struct fsverity_set {
+	__u64 offset;
+	__u64 flags;
+};
+
+/*
+ * TODO(ebiggers): why isn't this using the same type code as used in the
+ * fsverity_header?
+ */
+#define FS_VERITY_ROOT_HASH_ALGO_SHA256	0x0000
+
+/*
+ * TODO(ebiggers): rename this to 'struct fsverity_measurement' to avoid
+ * confusion with the Merkle tree root hash?
+ */
+struct fsverity_root_hash {
+	__u32 root_hash_algorithm;
+	__u32 flags;
+	__u8 reserved[4];
+	__u8 root_hash[64];
+};
+
+/*
+ * TODO(ebiggers): is there a less confusing name for this?  "measure" makes it
+ * sound like it's returning something...
+ */
+#define FS_IOC_MEASURE_FSVERITY		_IOW('f', 133, \
+					      struct fsverity_root_hash)
+#define FS_IOC_SET_FSVERITY		_IOW('f', 134, struct fsverity_set)
+
+#endif /* _FSVERITY_KERNEL_DEFS_H */