migrator: log directly to persistent storage

The initramfs logs default to being written to tmpfs at /run. The
migrator hook also writes messages to this location, which is later
copied to persistent storage by resin-init-flasher if present. However,
any failure before resin-init-flasher, such as failing to copy
installation binaries to memory, will result in the file not being
written to persistent storage for debugging.

Write the log file to persistent storage directly in the migrator hook
in case of failure before resin-init-flasher, but also write to tmpfs
and copy to the new boot partition filesystem in the flasher script.

This ensures the migration logfile is always available on persistent
storage no matter where a failure occurs.

Change-type: patch
Signed-off-by: Joseph Kogut <[email protected]>

meta-balena-common/recipes-core/initrdscripts/files/migrate

@@ -28,6 +28,8 @@
 
 # ensure logs are written and filesystems are unmounted before exiting
 cleanup() {
+    disable_persistent_logging
+
     sync
     umount -a
 }
@@ -117,8 +119,21 @@ cp_memsafe() {
     wait $pid
 }
 
+disable_persistent_logging() {
+    # stop redirection and kill tee before unmounting
+    exec 1>&3 2>&4
+    # shellcheck disable=SC2009
+    kill "$(ps | grep "${logfile}" | awk 'NR==1{print $1}')"
+}
+
 # Main module function
 migrate_run() {
+    # create a migration logfile in boot partition
+    logfile=migration_$(date +"%Y%m%dT%H%M").log
+    # duplicate stdout/stderr descriptors for later restoration
+    exec 3>&1 4>&2
+    exec &> >(tee "${FLASH_BOOT_MOUNT}/${logfile}")
+
     # Find the raw image in the rootfs partition
     image=$(find "${ROOTFS_DIR}" -xdev -type f -name "${BALENA_IMAGE}")
     kernel_images=$(find "${ROOTFS_DIR}" -xdev -type f -name "@@KERNEL_IMAGETYPE@@*")
@@ -186,7 +201,16 @@ migrate_run() {
         _config_json_name=$(basename "${CONFIG_PATH}")
         cp "${FLASH_BOOT_MOUNT}/${_config_json_name}" "${CONFIG_PATH}"
 
-        umount "${FLASH_BOOT_MOUNT}" > /dev/null || true
+        # disable writing of persistent log to flasher boot partition and
+        # unmount before migrating, as any block level writes while the
+        # partition is mounted can leave the filesystem in an inconsistent
+        # state
+        disable_persistent_logging
+        # attempt unmount several times, as it may not succeed immediately, but
+        # don't try forever, as it may leave the device unreachable
+        if ! timeout 10 bash -c "until umount ${FLASH_BOOT_MOUNT}; do sleep 1; done"; then
+            fail "Failed to umount ${FLASH_BOOT_MOUNT}"
+        fi
         sync "${EXTERNAL_DEVICE_BOOT_PART_MOUNTPOINT}"
         # Unmount the rootfs as we are going to program over
         umount "${ROOTFS_DIR}"

meta-balena-common/recipes-support/resin-init/resin-init-flasher/resin-init-flasher

@@ -473,7 +473,7 @@ info "Board specific flash procedure..."
 info "Log end"
 # Preserve logs when running from initramfs
 if [ -n "${INITRAMFS_LOGFILE}" ] && [ -f "${INITRAMFS_LOGFILE}" ]; then
-    cp -fv "${INITRAMFS_LOGFILE}" "${INTERNAL_DEVICE_BOOT_PART_MOUNTPOINT}/migration_$(date +"%Y%m%dT%H%M")"
+    cp -fv "${INITRAMFS_LOGFILE}" "${INTERNAL_DEVICE_BOOT_PART_MOUNTPOINT}/migration_$(date +"%Y%m%dT%H%M").log"
 fi
 
 umount $INTERNAL_DEVICE_BOOT_PART_MOUNTPOINT