rpm2img: stripe root filesystem

Aligning the root filesystem along 4MiB boundaries provides a subtle but
measureable performance improvement in Bottlerocket's boot process.

tools/rpm2img

@@ -126,6 +126,11 @@ VERITY_HASH_ALGORITHM=sha256
 VERITY_DATA_BLOCK_SIZE=4096
 VERITY_HASH_BLOCK_SIZE=4096
 
+# Bottlerocket has been experimentally shown to boot faster on EBS volumes when striping the root filesystem into 4MiB stripes.
+# We use 4kb ext4 blocks. The stride and stripe should both be $STRIPE_SIZE / $EXT4_BLOCK_SIZE
+ROOT_STRIDE=1024
+ROOT_STRIPE_WIDTH=1024
+
 case "${PARTITION_PLAN}" in
   split)
     truncate -s "${OS_IMAGE_SIZE_GIB}G" "${OS_IMAGE}"
@@ -279,7 +284,8 @@ mkdir -p "${ROOT_MOUNT}/lost+found"
 ROOT_LABELS=$(setfiles -n -d -F -m -r "${ROOT_MOUNT}" \
     "${SELINUX_FILE_CONTEXTS}" "${ROOT_MOUNT}" \
     | awk -v root="${ROOT_MOUNT}" '{gsub(root"/","/"); gsub(root,"/"); print "ea_set", $1, "security.selinux", $4}')
-mkfs.ext4 -O ^has_journal -b "${VERITY_DATA_BLOCK_SIZE}" -d "${ROOT_MOUNT}" "${ROOT_IMAGE}" "${partsize[ROOT-A]}M"
+mkfs.ext4 -E "lazy_itable_init=0,stride=${ROOT_STRIDE},stripe_width=${ROOT_STRIPE_WIDTH}" \
+  -O ^has_journal -b "${VERITY_DATA_BLOCK_SIZE}" -d "${ROOT_MOUNT}" "${ROOT_IMAGE}" "${partsize[ROOT-A]}M"
 echo "${ROOT_LABELS}" | debugfs -w -f - "${ROOT_IMAGE}"
 resize2fs -M "${ROOT_IMAGE}"
 dd if="${ROOT_IMAGE}" of="${OS_IMAGE}" conv=notrunc bs=1M seek="${partoff[ROOT-A]}"