contrib: add megaraid_sas unbind script

contrib/README.md

@@ -28,6 +28,10 @@ review the scripts themselves for more thorough descriptions of their use.
  early-setup hook, this facilitates, *e.g.*, multiple-slot keys for ZFS pools
  that use native encryption.
 
+- `megaraid-teardown.sh` - Unbind drivers for `megaraid_sas` devices, so that
+ they're available after a kexec. This is patterned after the XHCI teardown
+ script.
+
 - `remote-ssh-build.sh` - This is a standalone script intended to wrap the
  `zbm-builder.sh` image-builder script, incorporating a dropbear SSH server,
  host keys and an `authorized_keys` file that permit remote access and pool

contrib/megaraid-teardown.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+#
+# Configure this script as a user teardown.d hook
+#
+
+SYS_MEGARAID=/sys/bus/pci/drivers/megaraid_sas
+
+# shellcheck disable=SC2231
+for DEVPATH in ${SYS_MEGARAID}/????:??:??.?; do
+ [ -L "${DEVPATH}" ] || continue
+ DEVICE="${DEVPATH#"${SYS_MEGARAID}"/}"
+ echo "Tearing down Megaraid controller ${DEVICE}..."
+ echo "${DEVICE}" > ${SYS_MEGARAID}/unbind
+ echo "Resetting Megaraid controller ${DEVICE}..."
+ echo "1" > /sys/bus/pci/devices/${DEVICE}/reset
+done