diff --git a/include/spdk/fd.h b/include/spdk/fd.h
index 8fec287e2..8da7f2cd7 100644
--- a/include/spdk/fd.h
+++ b/include/spdk/fd.h
@@ -44,7 +44,22 @@
 extern "C" {
 #endif
 
+/**
+ * Get the file size.
+ *
+ * \param fd  File descriptor.
+ *
+ * \return    File size.
+ */
 uint64_t spdk_fd_get_size(int fd);
+
+/**
+ * Get the block size of the file.
+ *
+ * \param fd  File descriptor.
+ *
+ * \return    Block size.
+ */
 uint32_t spdk_fd_get_blocklen(int fd);
 
 #ifdef __cplusplus