Allow to update kexec-tools using virt-customize for cloud base image

Resolves: bz2089871

Currently, kexec-tools can't be updated using virt-customize because
older version of kdumpctl can't acquire instance lock for the
get-default-crashkernel subcommand. The reason is /var/lock is linked to
/run/lock which however doesn't exist in the case of virt-customize.

This patch fixes this problem by using /tmp/kdump.lock as the lock
file if /run/lock doesn't exist.

Note
1. The lock file is now created in /run/lock instead of /var/run/lock since
   Fedora has adopted adopted /run [2] since F15.
2. %pre scriptlet now always return success since package update won't
   be blocked

[1] https://fedoraproject.org/wiki/Features/var-run-tmpfs

Fixes: 0adb0f4 ("try to reset kernel crashkernel when kexec-tools updates the default crashkernel value")

Reported-by: Nicolas Hicher <nhicher@redhat.com>
Suggested-by: Laszlo Ersek <lersek@redhat.com>
Suggested-by: Philipp Rudo <prudo@redhat.com>
Signed-off-by: Coiby Xu <coxu@redhat.com>
Reviewed-by: Philipp Rudo <prudo@redhat.com>

kdumpctl

@@ -49,9 +49,16 @@ fi
 
 single_instance_lock()
 {
-	local rc timeout=5
+	local rc timeout=5 lockfile
 
-	if ! exec 9> /var/lock/kdump; then
+	if [[ -d /run/lock ]]; then
+		lockfile=/run/lock/kdump
+	else
+		# when updating package using virt-customize, /run/lock doesn't exist
+		lockfile=/tmp/kdump.lock
+	fi
+
+	if ! exec 9> $lockfile; then
 		derror "Create file lock failed"
 		exit 1
 	fi

kexec-tools.spec

@@ -269,6 +269,8 @@ if ! grep -qs "ostree" /proc/cmdline && [ $1 == 2 ] && grep -q get-default-crash
   kdumpctl get-default-crashkernel fadump > /tmp/old_default_crashkernel_fadump 2>/dev/null
 %endif
 fi
+# don't block package update
+:
 
 %post
 # Initial installation