os-helpers: add a helper function to generate fingerprint files

This function will be re-used as it's called from the HUP hooks and
from the flasher image for secure boot devices that split boot
partitions.

Change-type: patch
Signed-off-by: Alex Gonzalez <alexg@balena.io>

meta-balena-common/recipes-support/os-helpers/os-helpers.bb

@@ -55,6 +55,7 @@ do_install() {
         ${WORKDIR}/safe_reboot \
         ${D}${libexecdir}
         sed -i "s,@@BALENA_CONF_UNIT_STORE@@,${BALENA_CONF_UNIT_STORE},g" ${D}${libexecdir}/os-helpers-config
+        sed -i -e "s,@@BALENA_FINGERPRINT_FILENAME@@,${BALENA_FINGERPRINT_FILENAME},g" -e "s,@@BALENA_FINGERPRINT_EXT@@,${BALENA_FINGERPRINT_EXT},g" ${D}${libexecdir}/os-helpers-fs
 }
 
 FILES:${PN}-fs = "${libexecdir}/os-helpers-fs"

meta-balena-common/recipes-support/os-helpers/os-helpers/os-helpers-fs

@@ -313,3 +313,24 @@ wait4udev() {
 
     return 0
 }
+
+# Generates a fingerprint file on the fly for boot partitions,
+# ignoring config.json files.
+# Arguments:
+#   Directoty path - trailing slashes are removed
+# Output:
+#   A ${BALENA_FINGERPRINT_FILENAME}/${BALENA_FINGERPRINT_EXT} file where
+#   entries have no path prefix.
+generate_bootpart_fingerprint() {
+    FSDIR="${1%/}"
+    tmpfp=$(mktemp)
+    info "Generating fingerprint file for $FSDIR"
+    rm -rf ${FSDIR}/@@BALENA_FINGERPRINT_FILENAME@@.@@BALENA_FINGERPRINT_EXT@@
+    find ${FSDIR} -xdev -type f \
+        ! -name @@BALENA_FINGERPRINT_FILENAME@@.@@BALENA_FINGERPRINT_EXT@@ \
+        ! -name config.json \
+        -exec md5sum {} \; | sed "s#${FSDIR}/##g" | \
+        sort -k2 > "${tmpfp}"
+        mv "${tmpfp}" ${FSDIR}/@@BALENA_FINGERPRINT_FILENAME@@.@@BALENA_FINGERPRINT_EXT@@
+        sync -f "${FSDIR}"
+}