diff --git a/src/core/osmo_io.c b/src/core/osmo_io.c
index f23986f..649bf73 100644
--- a/src/core/osmo_io.c
+++ b/src/core/osmo_io.c
@@ -323,6 +323,10 @@
 	iofd->pending = pending;
 }
 
+/*! completion handler: Called by osmo_io backend after a given I/O operation has completed
+ *  \param[in] iofd I/O file-descriptor on which I/O has completed
+ *  \param[in] msg message buffer containing data related to completed I/O
+ *  \param[in] hdr serialized msghdr containing state of completed I/O */
 void iofd_handle_recv(struct osmo_io_fd *iofd, struct msgb *msg, int rc, struct iofd_msghdr *hdr)
 {
 	talloc_steal(iofd->msgb_alloc.ctx, msg);