script and udev rule for deterministic ephemeral devices

999-aws-ebs-nvme.rules

@@ -1 +1,2 @@
 SUBSYSTEM=="block", KERNEL=="nvme[0-9]*n1", ATTRS{model}=="Amazon Elastic Block Store", PROGRAM+="/usr/local/sbin/ebs-nvme-mapping.sh /dev/%k" SYMLINK+="%c"
+KERNEL=="nvme[0-9]*n[0-9]*", ENV{DEVTYPE}=="disk", ATTRS{model}=="Amazon EC2 NVMe Instance Storage", PROGRAM="/usr/local/bin/nextephemeraldevice.sh %k", SYMLINK+="%c"

nextephemeraldevice.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# To be used with the udev rule: /etc/udev/rules.d/999-aws-ebs-nvme.rules
+
+# check if lock file exists
+script_name="$(basename $0)"
+pid_file="/tmp/${script_name}.lock"
+counter=0
+until [ $counter -eq 5 ] || [[ ! -e "${pid_file}" ]] ; do
+  sleep $(( counter++ ))
+done
+
+# create lock file if it does not exist
+if [[ -e "${pid_file}" ]]; then
+  echo "Lock file ${pid_file} still exists after counter ended" >&2
+  exit 1
+else
+  touch "${pid_file}"
+fi
+
+kern_name=${1}
+incr=0
+while [[ -e "/dev/ephemeral${incr}" ]] && [[ $(readlink "/dev/ephemeral${incr}") != "${kern_name}" ]]; do
+  incr=$[$i+1]
+done
+# remove lock file
+rm "${pid_file}"
+echo "ephemeral${incr}"