Improves documentation

 * Describes better available source tree sharing method (between
xds-agent and xds-server), and which to prefer depending on the
deployment setup.
 * Gives indication about how to pass RSYNC_TARGET and RSYNC_PREFIX
 env vars to the helloworld-native-application build process.
 * Swap chapter order (build before config)

Change-Id: Ie4c22f277a59b0405744d71b0fadff67c5d5d025
Signed-off-by: Johann CAHIER <johann.cahier@iot.bzh>

1 files changed, 86 insertions, 0 deletions

diff --git a/docs/part-2/4_xds-gdb/2_config.md b/docs/part-2/4_xds-gdb/2_config.md
new file mode 100644
index 0000000..8568f18
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+# Configuration
+
+`xds-gdb` configuration is defined by variables (see listed below).
+
+These variables may be set using:
+
+- environment variables (inherited),
+- or a config file set with `XDS_CONFIG` environment variable, for example:
+  `XDS_CONFIG=/tmp/my_xds_gdb_config.env xds-gdb`
+- or by setting variables within a gdb ini file (see details below),
+- or a "user" config file located in following directory (first found is taken):
+  1. $(CURRENT_DIRECTORY)/.xds-gdb.env
+  1. $(CURRENT_DIRECTORY)/../xds-gdb.env
+  1. $(CURRENT_DIRECTORY)/target/xds-gdb.env
+  1. $(HOME)/.config/xds/xds-gdb.env
+
+## Configuration Variables
+
+`XDS_CONFIG`
+
+Config file defining `XDS_xxx` configuration variables.
+
+Variables of this file will overwrite inherited environment variables.
+
+Variables definition may be prefixed or not by "export" keyword.
+
+Here is an example of config file:
+
+```bash
+cat $HOME/myProject/xds-gdb.env
+
+export XDS_AGENT_URL=http://localhost:8800
+export XDS_PROJECT_ID=4021617e-ced0-11e7-acd2-3c970e49ad9b
+export XDS_SDK_ID=c226821b-b5c0-386d-94fe-19f807946d03
+```
+
+`XDS_LOGLEVEL`
+
+Set logging level
+
+Supported levels:
+
+- panic
+- fatal
+- error
+- warn
+- info
+- debug
+
+`XDS_LOGFILE`
+
+Set logging file, default `/tmp/xds-gdb.log`.
+
+`XDS_NATIVE_GDB`
+
+Use native gdb mode instead of XDS mode.
+
+`XDS_PROJECT_ID`  *(mandatory in XDS mode)*
+
+Project ID you want to build
+
+`XDS_RPATH`
+
+Relative path into project
+
+`XDS_SDK_ID`   *(mandatory in XDS mode)*
+
+Cross Sdk ID to use to build project
+
+`XDS_AGENT_URL`
+
+Local XDS agent url (default `http://localhost:8800`)
+
+## Configuration variables set within gdb init command file
+
+Above `XDS_xxx` variables may also be defined within gdb init command file
+(see --command or -x option of genuine Gdb).
+
+You must respect the following syntax: commented line including `:XDS-ENV:` tag
+
+Example of gdb init file where we define project and sdk ID:
+
+```bash
+     # :XDS-ENV: XDS_PROJECT_ID=4021617e-ced0-11e7-acd2-3c970e49ad9b
+     # :XDS-ENV: XDS_SDK_ID=c226821b-b5c0-386d-94fe-19f807946d03
+```