[master] 424f2c6b3 whats-new: First pass on upgrade notes

[Dridi Boukelmoune]

commit 424f2c6b3b79f4065d98ff92c4d967a024a02d34
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Mon Mar 6 14:42:04 2023 +0100

    whats-new: First pass on upgrade notes

diff --git a/doc/sphinx/whats-new/changes-trunk.rst b/doc/sphinx/whats-new/changes-trunk.rst
index 9fddc2441..4df5b8236 100644
--- a/doc/sphinx/whats-new/changes-trunk.rst
+++ b/doc/sphinx/whats-new/changes-trunk.rst
@@ -164,4 +164,12 @@ Custom backend implementations are now in charge of printing headers, which
 avoids duplicates when a custom implementation relied on ``http_*()`` that
 would also log the headers being set up.
 
+The ``VRT_new_backend*()`` functions take an additional backend argument, the
+optional via backend. It can not be a custom backend implementation, but it
+can be a director resolving a native backend.
+
+There is a new ``authority`` field for via backends in ``struct vrt_backend``.
+
+There is a new ``exp_close`` field in ``struct vrt_backend_probe``.
+
 *eof*
diff --git a/doc/sphinx/whats-new/upgrading-trunk.rst b/doc/sphinx/whats-new/upgrading-trunk.rst
index 6143fde99..6a2f56cff 100644
--- a/doc/sphinx/whats-new/upgrading-trunk.rst
+++ b/doc/sphinx/whats-new/upgrading-trunk.rst
@@ -30,4 +30,37 @@ to:**
 * Changes in public APIs that may require changes in VMODs or VAPI/VUT
   clients.
 
+New VSL format
+==============
+
+The binary format of Varnish logs changed to increase the space for VXIDs from
+32 bits to 64. This is not a change that older versions of the Varnish logging
+utilities can understand, and the new utilities can also not process old logs.
+
+There is no conversion tool from the old format to the new one, so this should
+become a problem only when raw logs are stored for future processing. If old
+binary logs need to remain usable, the only solution is to use a compatible
+Varnish version and at the time of this release, the 6.0 branch is the only
+one without an EOL date.
+
+Via backends
+============
+
+The new backend argument to the ``VRT_new_backend*()`` functions is optional
+and ``NULL`` can be passed to match the previous behavior.
+
+suckaddr
+========
+
+The following functions return or accept ``const`` pointers from now on:
+
+- ``VSA_Clone()``
+- ``VSA_getsockname()``
+- ``VSA_getpeername()``
+- ``VSA_free()``
+- ``VSA_Malloc()``
+- ``VSA_Build*()``
+- ``VSS_ResolveOne()``
+- ``VSS_ResolveFirst()``
+
 *eof*