lib: rework check_bootcounter to support legacy

New `uboot.cnt` file format appears in u-boot 2019.01+dfsg-7co7.
Allow to read legacy format.
If "magic" and "version" are not requested explicitly the function
accept any supported `uboot.cnt` format.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

run-test-ota-rollback-blacklist.sh

@@ -51,7 +51,7 @@ phase_check_update()
 
 	# Check the bootcounter state
 	# It may have different boot count on different boards due LAVA
-	check_bootcounter bd 01 "" 01
+	check_bootcounter "" "" "" 01
 
 	# Emulate the ugrade state -- set the upgrade flag and bootcounter to any value above the limit
 	# This should to trigger the U-Boot to boot previous version after reboot
@@ -81,7 +81,7 @@ phase_check_rollback()
 
 	# after the rollback, the apertis update manager resets the bootcount
 	# Ensure to have non-upgrade state
-	check_bootcounter bd 01 00 00
+	check_bootcounter "" "" 00 00
 
 	# Must exists and contain "failed" upgrade
 	cat /var/aum_blacklist.conf

run-test-rollback-blacklist.sh

@@ -19,7 +19,7 @@ phase_boot()
 	ostree admin status
 
 	# Ensure to have upgrade state
-	check_bootcounter bd 01 00 01
+	check_bootcounter "" "" 00 01
 }
 
 phase_check_update()
@@ -43,7 +43,7 @@ phase_check_update()
 
 	# Check the bootcounter state
 	# It may have different boot count on different boards due LAVA
-	check_bootcounter bd 01 "" 01
+	check_bootcounter "" "" "" 01
 
 	# Emulate the ugrade state -- set the upgrade flag and bootcounter to any value above the limit
 	# This should to trigger the U-Boot to boot previous version after reboot
@@ -73,7 +73,7 @@ phase_check_rollback()
 
 	# after the rollback, the apertis update manager resets the bootcount
 	# Ensure to have non-upgrade state
-	check_bootcounter bd 01 00 00
+	check_bootcounter "" "" 00 00
 
 	cat /var/aum_blacklist.conf
 }

update-manager-common.sh

@@ -316,6 +316,17 @@ check_bootcounter()
 	od -t x1 -An /boot/uboot.cnt | (
 		read -r m ver cnt uflag
 
+		# Special case for old format
+		if [ "$m" = "bc" ]; then
+			cnt="$ver"
+			ver="00"
+			# NB: due the bug in legacy U-Boot -- it always create the uboot.cnt and
+			# increase the counter, so it is not possible to detect the upgrade
+			# state properly. Hence set the upgrade state for the legacy into
+			# requested value to avoid failures.
+			uflag="${4:-1}"
+		fi
+
 		local ret=0
 		local magic="${1:-$m}"
 		local version="${2:-$ver}"