From 5bdb4820b0eddf1d7f3a4a25a74819844e06e7a1 Mon Sep 17 00:00:00 2001
From: Pete Fotheringham <pete.fotheringham@codethink.co.uk>
Date: Fri, 12 Dec 2014 11:36:04 +0000
Subject: Document KERNEL_ARGS write extension parameter

---
 morphlib/exts/kvm.write.help            | 9 +++++++++
 morphlib/exts/rawdisk.write.help        | 9 +++++++++
 morphlib/exts/virtualbox-ssh.write.help | 9 +++++++++
 morphlib/writeexts.py                   | 6 ++++++
 4 files changed, 33 insertions(+)

diff --git a/morphlib/exts/kvm.write.help b/morphlib/exts/kvm.write.help
index 8ddcb89c..04393b8a 100644
--- a/morphlib/exts/kvm.write.help
+++ b/morphlib/exts/kvm.write.help
@@ -63,5 +63,14 @@ help: |
         allowed values =
         - 'extlinux'
 
+    * KERNEL_ARGS=args: optional additional kernel command-line parameters to
+      be appended to the default set. The default set is:
+
+        'rw init=/sbin/init rootfstype=btrfs \
+          rootflags=subvol=systems/default/run \
+          root=[name or UUID of root filesystem]'
+
+        (See https://www.kernel.org/doc/Documentation/kernel-parameters.txt)
+
     (See `morph help deploy` for details of how to pass parameters to write
     extensions)
diff --git a/morphlib/exts/rawdisk.write.help b/morphlib/exts/rawdisk.write.help
index d6c78573..54af81c4 100644
--- a/morphlib/exts/rawdisk.write.help
+++ b/morphlib/exts/rawdisk.write.help
@@ -55,5 +55,14 @@ help: |
         allowed values =
         - 'extlinux'
 
+    * KERNEL_ARGS=args: optional additional kernel command-line parameters to
+      be appended to the default set. The default set is:
+
+        'rw init=/sbin/init rootfstype=btrfs \
+          rootflags=subvol=systems/default/run \
+          root=[name or UUID of root filesystem]'
+
+        (See https://www.kernel.org/doc/Documentation/kernel-parameters.txt)
+
     (See `morph help deploy` for details of how to pass parameters to write
     extensions)
diff --git a/morphlib/exts/virtualbox-ssh.write.help b/morphlib/exts/virtualbox-ssh.write.help
index 4dddd987..cb50acc0 100644
--- a/morphlib/exts/virtualbox-ssh.write.help
+++ b/morphlib/exts/virtualbox-ssh.write.help
@@ -62,6 +62,15 @@ help: |
         allowed values =
         - 'extlinux'
 
+    * KERNEL_ARGS=args: optional additional kernel command-line parameters to
+      be appended to the default set. The default set is:
+
+        'rw init=/sbin/init rootfstype=btrfs \
+          rootflags=subvol=systems/default/run \
+          root=[name or UUID of root filesystem]'
+
+        (See https://www.kernel.org/doc/Documentation/kernel-parameters.txt)
+
     * AUTOSTART=<VALUE> - boolean. If it is set, the VM will be started when
       it has been deployed.
 
diff --git a/morphlib/writeexts.py b/morphlib/writeexts.py
index fd2f5529..6ab2dd55 100644
--- a/morphlib/writeexts.py
+++ b/morphlib/writeexts.py
@@ -474,6 +474,12 @@ class WriteExtension(cliapp.Application):
 
         self.status(msg='Creating extlinux.conf')
         config = os.path.join(real_root, 'extlinux.conf')
+
+        ''' Please also update the documentation in the following files
+            if you change these default kernel args:
+            - kvm.write.help
+            - rawdisk.write.help
+            - virtualbox-ssh.write.help '''
         kernel_args = (
             'rw ' # ro ought to work, but we don't test that regularly
             'init=/sbin/init ' # default, but it doesn't hurt to be explicit
-- 
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