feat(updater): step lines for the six stages of an install

The factory marked its own steps and then went silent for the minutes the
updater takes - unpacking a rootfs and writing a boot chain looked like a hang
on the terminal, because everything perform_update.sh printed went to the log.

Six lines now: clearing the slot, fetching, unpacking, first boot, kernel and
boot chain, and the slot that came out. They carry the same "==>" marker as
image-factory/create_image.sh and are not indented - tool.sh's nested_step adds
the indent when it lifts a factory line to the terminal, so indenting here
would double it. On a device the marker is a prefix in the journal.

The steps sit in main(), not in the functions, so the functions stay quiet for
the tests that read their output.

Verified by running main() end to end against mocked docker, tar, btrfs, df and
a stand-in rootfs: slot B in, slot A written, fstab with subvol=@os/system-A in
the slot, first-run.sh and install-kernel.sh called with the slot and digest,
exit 0. That path has no test of its own - it is the main() gap the suite
leaves open.

Signed-off-by: Simon Walz <contact@simonwalz.de>

Author: simonwalz

updater/perform_update.sh

@@ -33,6 +33,15 @@ raise_info() {
   exit "$code"
 }
 
+# One line per step, marked for whoever is watching. cuos-release/tool.sh puts
+# lines carrying this marker on the terminal - indented by itself, so this one
+# does not - and everything else in output/NAME.build.log. On a device the
+# marker is just a prefix in the journal. Keep it in step with
+# image-factory/create_image.sh and log_is_step_line() over there.
+step() {
+  echo "==> $*"
+}
+
 # Fields counted from the end: df puts a device name that does not fit on a
 # line of its own.
 disk_usage() {
@@ -323,8 +332,12 @@ main() {
     raise_info 102 "No OS update available"
   fi
 
+  step "Clearing slot ${SLOT}"
   prepare_slot
 
+  if ! is_local_build; then
+    step "Fetching ${IMAGE}"
+  fi
   pull_image
 
   NEW_DIGEST="$(repo_digest)"
@@ -345,12 +358,15 @@ main() {
     raise 105 "Failed to get image digest"
   fi
 
+  step "Unpacking the system into slot ${SLOT}"
   export_rootfs
 
   write_fstab
 
+  step "Preparing the first boot"
   run_first_run
 
+  step "Installing the kernel and the boot chain"
   install_kernel
 
   report_disk_usage "after"
@@ -361,6 +377,8 @@ main() {
     check_boot_reserve
   fi
 
+  step "Slot ${SLOT} installed: ${IMAGE}"
+
   exit 0
 }