Add some prose on backend autodetection

Change-Id: Ibc37f99cba8f51a3bdd40007928b469c733242eb

diff --git a/documentation/overview.rst b/documentation/overview.rst
index a6eaed3..377d575 100644 (file)
--- a/documentation/overview.rst
+++ b/documentation/overview.rst
@@ -91,6 +91,19 @@ Here's a comparison:
                │ kernel code and the internal  │ userspace and the internal
                │ format is fairly rigid.       │ format is forward-compatible.
 
+Traditionally, the backend needed to be set in advance in a config file; in the
+default configs it has been set to pipe, with a separate package switching it to
+logger. However, we decided to introduce backend autodetection. It is brutally
+simple: we try to open the main buffer of the logger backend. If it succeeds, we
+use the logger backend, and if it doesn't, we use the pipe backend.
+
+The autodetection is not only for simplicity; in Tizen IoT images, the kernel
+and modules are different for each target, but the root filesystem is shared.
+The DLog config is part of the root filesystem, and so is shared between all the
+targets. This means that, since some of the targets don't support the logger
+backend, all the devices needed to use the pipe backend by default, even though
+the logger backend is usually a somewhat better choice.
+
 dlog_logger interface
 ---------------------