upstream: add a comment describing the ranges of channel IDs that

we use; requested by markus@

OpenBSD-Commit-ID: 83a1f09810ffa3a96a55fbe32675b34ba739e56b

1 files changed, 9 insertions, 1 deletions

diff --git a/channels.h b/channels.h
index aa2a87c10..c8ae0d904 100644
--- a/channels.h
+++ b/channels.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.h,v 1.132 2018/10/04 00:10:11 djm Exp $ */
+/* $OpenBSD: channels.h,v 1.133 2020/01/25 22:49:38 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -105,8 +105,16 @@ struct channel_connect {
 /* Callbacks for mux channels back into client-specific code */
 typedef int mux_callback_fn(struct ssh *, struct Channel *);
 
+/*
+ * NB. channel IDs on the wire and in c->remote_id are uint32, but local
+ * channel IDs (e.g. c->self) only ever use the int32 subset of this range,
+ * because we use local channel ID -1 for housekeeping. Remote channels have
+ * a dedicated "have_remote_id" flag to indicate their validity.
+ */
+
 struct Channel {
         int     type;           /* channel type/state */
+
         int     self;           /* my own channel identifier */
         uint32_t remote_id;     /* channel identifier for remote peer */
         int     have_remote_id; /* non-zero if remote_id is valid */