base-files: fwtool: implement compatibility check for images

We regularly encounter the situation that devices are subject to
changes that will make them incompatible to previous versions.
Removing SUPPORTED_DEVICES will not really be helpful in most of these
cases, as this only helps after a rename.

To solve this situation, this patchset introduces a compatibility
version for devices. In this patch, the actual checks are implemented
into fwtool_check_image():

If an incompatible change is introduced, one can increase either
the minor version (1.0->1.1) or the major version (1.0->2.0).

Minor version increment:
This will still allow sysupgrade, but require to reset config
(-n or SAVE_CONFIG=0). If sysupgrade is called without -n, a
corresponding message will be printed. If sysupgrade is called
with -n, it will just pass, with supported devices being checked
as usual. (Which will allow us to add back SUPPORTED_DEVICES for
many cases.)

Major version increment:
This is meant for potential (rare) cases where sysupgrade is
not possible at all, because it would break the device.
In this case, a warning will be printed, and -n won't help.

If image check fails because of one of the versions parts not
matching, the content of DEVICE_COMPAT_MESSAGE is printed in
addition to the generic message (if set).

For both cases, upgrade can still be forced with -F as usual.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

package/base-files/files/lib/upgrade/fwtool.sh

@@ -44,13 +44,35 @@ fwtool_check_image() {
 	}
 
 	device="$(cat /tmp/sysinfo/board_name)"
+	devicecompat="$(uci -q get system.@system[0].compat_version)"
+	[ -n "$devicecompat" ] || devicecompat="1.0"
+
+	json_get_var imagecompat compat_version
+	json_get_var compatmessage compat_message
+	[ -n "$imagecompat" ] || imagecompat="1.0"
 
 	json_select supported_devices || return 1
 
 	json_get_keys dev_keys
 	for k in $dev_keys; do
 		json_get_var dev "$k"
-		[ "$dev" = "$device" ] && return 0
+		if [ "$dev" = "$device" ]; then
+			# major compat version -> no sysupgrade
+			if [ "${devicecompat%.*}" != "${imagecompat%.*}" ]; then
+				echo "The device is supported, but this image is incompatible for sysupgrade based on the image version ($devicecompat->$imagecompat)."
+				[ -n "$compatmessage" ] && echo "$compatmessage"
+				return 1
+			fi
+
+			# minor compat version -> sysupgrade with -n required
+			if [ "${devicecompat#.*}" != "${imagecompat#.*}" ] && [ "$SAVE_CONFIG" = "1" ]; then
+				echo "The device is supported, but the config is incompatible to the new image ($devicecompat->$imagecompat). Please upgrade without keeping config (sysupgrade -n)."
+				[ -n "$compatmessage" ] && echo "$compatmessage"
+				return 1
+			fi
+
+			return 0
+		fi
 	done
 
 	echo "Device $device not supported by this image"