contrib/fedora-default-kernel: Make more robust and add rEFInd support

Add a script to explicitly handle multiple Surface kernel versions being
installed in parallel, sorting kernels by timestamp and choosing the
latest one.

Further, add support for rEFInd by updating the vmlinuz file timestamp
to ensure it's always seen as the last modified file (which will be
picked by rEFInd as the "default" kernel in that directory).

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>

contrib/fedora-default-kernel/README.md

@@ -12,6 +12,8 @@ selection every time.
 ```bash
 $ sudo dnf install /usr/sbin/grubby
 $ sudo cp default-kernel.{path,service} /etc/systemd/system/
+$ sudo cp default-kernel.sh /usr/local/bin/default-kernel
+$ sudo chmod 755 /usr/local/bin/default-kernel
 $ sudo systemctl daemon-reload
 $ sudo systemctl enable --now default-kernel.path
 ```

contrib/fedora-default-kernel/default-kernel.service

@@ -3,4 +3,4 @@ Description=linux-surface default kernel watchdog
 
 [Service]
 Type=oneshot
-ExecStart=/bin/sh -c "grubby --set-default /boot/vmlinuz*surface*"
+ExecStart=/usr/local/bin/default-kernel

contrib/fedora-default-kernel/default-kernel.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+set -euo pipefail
+
+# get list of surface kernels with timestamp
+kernels=$(find /boot -maxdepth 1 -name "vmlinuz-*.surface.*" -printf '%T@\t%p\n')
+
+# sort by timestamp
+kernels=$(echo "${kernels}" | sort -n)
+
+# get latest kernel (last line) and extract path
+kernel=$(echo "${kernels}" | tail -n1 | cut -f2)
+
+echo $kernel
+
+# update GRUB config
+grubby --set-default "${kernel}"
+
+# update timestamp for rEFInd (ensure it's marked as latest across all kernels,
+# not just surface ones)
+touch "${kernel}"