From 6b479b657266f130e6dc343817986e88883cabaf Mon Sep 17 00:00:00 2001
From: Kairui Song <kasong@redhat.com>
Date: Wed, 25 Jul 2018 18:55:00 +0800
Subject: [PATCH] kdumpctl: Rebuild initramfs if loaded kernel modules changed

Currently, we only rebuilt kdump initramfs on config file change,
fs change, or watchdog related change. This will not cover the case
that hardware changed but fs layout and other configurations still
stays the same, and kdump may fail.

To cover such case, we can detect and compare loaded kernel modules,
if a hardware change requires the image to be rebuilt, loaded kernel
modules must have changed.

Starting from commit 7047294 dracut will record loaded kernel modules
when the image is built if hostonly mode is enabled.  With this patch,
kdumpctl will compare the recorded value with currently loaded kernel
modules, and rebuild the image on change.

"kdumpctl start" will be a bit slower, as we have to call lsinitrd one
more time to get the loaded kernel modules list. I measure the time
consumption and we have an overall 0.2s increased loading time.

Time consumption of command "kdumpctl restart":

Before:
real    0m0.587s
user    0m0.481s
sys     0m0.102s

After:
real    0m0.731s
user    0m0.591s
sys     0m0.133s

Time comsumption of command "kdumpctl restart" with image rebuild:

Before (force rebuild):
real    0m10.972s
user    0m8.966s
sys     0m1.318s

After (inserted ~100 new modules):
real    0m11.220s
user    0m9.387s
sys     0m1.337s

Signed-off-by: Kairui Song <kasong@redhat.com>
---
 kdumpctl | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/kdumpctl b/kdumpctl
index 13b8209..6a01c13 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -458,6 +458,31 @@ check_wdt_modified()
 	return 1
 }
 
+check_kmodules_modified()
+{
+	# always sort again to avoid LANG/LC inconsistent problem
+	local _old_modules="$(lsinitrd $TARGET_INITRD -f /usr/lib/dracut/loaded-kernel-modules.txt | sort)"
+	local _new_modules="$(get_loaded_kernel_modules | sort)"
+
+	[[ -z $_old_modules ]] && echo "Warning: Previous loaded kernel module list is absent or empty"
+
+	local _added_modules=$(comm -13 <(echo "$_old_modules") <(echo "$_new_modules"))
+	local _dropped_modules=$(comm -23 <(echo "$_old_modules") <(echo "$_new_modules"))
+
+	if [ "$_old_modules" != "$_new_modules" ]; then
+		echo "Detected change(s) of loaded kernel modules list:"
+		[[ -n $_added_modules ]] && for _module in $_added_modules; do
+			echo "	+$_module"
+		done
+		[[ -n $_dropped_modules ]] && for _module in $_dropped_modules; do
+			echo "	-$_module"
+		done
+		return 1
+	fi
+
+	return 0
+}
+
 # returns 0 if system is not modified
 # returns 1 if system is modified
 # returns 2 if system modification is invalid
@@ -485,6 +510,11 @@ check_system_modified()
 		return 1
 	fi
 
+	check_kmodules_modified
+	if [ $? -ne 0 ]; then
+		return 1
+	fi
+
 	return 0
 }