[PATCH 1/2] kdumpctl: Add kdumpctl reset-crashkernel

[Kairui Song]

In newer kernel, crashkernel.conf will contain the default crashkernel
value of a kernel build. So introduce a new sub command to help user
reset kernel crashkernel size to the default value.

Signed-off-by: Kairui Song <kasong(a)redhat.com&gt;
---
 kdumpctl   | 33 +++++++++++++++++++++++++++++++--
 kdumpctl.8 |  9 +++++++++
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/kdumpctl b/kdumpctl
index 978dae5..f5b6a7f 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -1340,6 +1340,32 @@ do_estimate() {
 	fi
 }
 
+reset_crashkernel() {
+	local kernel=$1 entry crashkernel_conf
+	local grub_etc_default="/etc/default/grub"
+
+	[[ -z "$kernel" ]] && kernel=$(uname -r)
+	crashkernel_conf=$(cat "/usr/lib/modules/$kernel/crashkernel.conf"
2>/dev/null)
+
+	if [[ -z "$crashkernel_conf" ]]; then
+		derror "$kernel doesn't have a crashkernel.conf"
+		exit 1
+	fi
+
+	entry=$(grubby --info ALL | grep "^kernel=.*$kernel")
+	entry=${entry#kernel=}
+	entry=${entry#\"}
+	entry=${entry%\"}
+
+	if [[ -f "$grub_etc_default" ]]; then
+		sed -i -e "s/^\(GRUB_CMDLINE_LINUX=.*\)crashkernel=[^\ \"]*\([\
\"].*\)$/\1$crashkernel_conf\2/" "$grub_etc_default"
+	fi
+
+	[[ -f /etc/zipl.conf ]] && zipl_arg="--zipl"
+	grubby --args "$crashkernel_conf" --update-kernel "$entry"
$zipl_arg
+	[[ $zipl_arg ]] && zipl > /dev/null
+}
+
 if [ ! -f "$KDUMP_CONFIG_FILE" ]; then
 	derror "Error: No kdump config file found!"
 	exit 1
@@ -1398,8 +1424,11 @@ main ()
 	  estimate)
 		do_estimate
 		;;
+	  reset-crashkernel)
+		reset_crashkernel "$2"
+		;;
 	  *)
-		dinfo $"Usage: $0
{estimate|start|stop|status|restart|reload|rebuild|propagate|showmem}"
+		dinfo $"Usage: $0
{estimate|start|stop|status|restart|reload|rebuild|reset-crashkernel|propagate|showmem}"
 		exit 1
 	esac
 }
@@ -1409,6 +1438,6 @@ single_instance_lock
 
 # To avoid fd 9 leaking, we invoke a subshell, close fd 9 and call main.
 # So that fd isn't leaking when main is invoking a subshell.
-(exec 9<&-; main $1)
+(exec 9<&-; main "$@")
 
 exit $?
diff --git a/kdumpctl.8 b/kdumpctl.8
index a32a972..844601e 100644
--- a/kdumpctl.8
+++ b/kdumpctl.8
@@ -49,6 +49,15 @@ Prints the size of reserved memory for crash kernel in megabytes.
 Estimate a suitable crashkernel value for current machine. This is a
 best-effort estimate. It will print a recommanded crashkernel value
 based on current kdump setup, and list some details of memory usage.
+.TP
+.I reset-crashkernel [KERNEL]
+Reset crashkernel value to default value. kdumpctl will try to read
+from /usr/lib/modules/<KERNEL>/crashkernel.conf and reset specified
+kernel's crashkernel cmdline value. If no kernel is
+specified, will reset current running kernel's crashkernel value.
+If /usr/lib/modules/<KERNEL>/crashkernel.conf doesn't exist, will
+simply exit return 1.
+
 
 .SH "SEE ALSO"
 .BR kdump.conf (5),
-- 
2.31.1