[PATCH v2 4/6] base-files: fwtool: make compat_version backward compatible

[Adrian Schmutzler]

So far, the compatibility mechanism only works if both device and
image are already updated to the new routines. This patch extends
the sysupgrade metadata and fwtool_check_image() to account for
"older" images as well:

The basic mechanism for older devices to check for image compatibility
is the supported_devices entry. This can be exploited by putting
a custom message into this variable of the metadata, so older FW
will produce a mismatch and print the message as it thinks it's the
list of supported devices. So, we have two cases:

device 1.0, image 1.0:
  The metadata will just contain supported_devices as before.

device 1.0, image 1.1:
  The metadata will contain:

  "new_supported_devices":["device_string1", "device_string2", ...],
  "supported_devices":["Upgrade incompatible. Please check Wiki ..."]

  If the device is "legacy", i.e. does not have the updated fwtool.sh,
  it will just fail with image check and print the content of
  supported_devices. Upgrade can still be performed with -F like when
  SUPPORTED_DEVICES has been removed to prevent bricking.

  If the device has updated fwtool.sh (but is 1.0), it will just use
  the new_supported_devices instead, and work as intended (flashing
  with -n will work, flashing without will print the appropriate
  warning).

This mechanism should provide a fair tradeoff between simplicity
and functionality.

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

---

Changes in v2:
- Add DEVICE_COMPAT_MESSAGE and reword comment for legacy warning.
---
 include/image-commands.mk                      | 5 ++++-
 package/base-files/files/lib/upgrade/fwtool.sh | 7 ++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/image-commands.mk b/include/image-commands.mk
index 9da712e733..e21472a659 100644
--- a/include/image-commands.mk
+++ b/include/image-commands.mk
@@ -393,7 +393,10 @@ metadata_json = \
 		"metadata_version": "1.0", \
 		"compat_version": "$(call json_quote,$(compat_version))", \
 		$(if $(DEVICE_COMPAT_MESSAGE),"compat_message": "$(call json_quote,$(DEVICE_COMPAT_MESSAGE))"$(comma)) \
-		"supported_devices":[$(call metadata_devices,$(SUPPORTED_DEVICES))], \
+		$(if $(filter-out 1.0,$(compat_version)),"new_supported_devices":[$(call metadata_devices,$(SUPPORTED_DEVICES))]$(comma)) \
+		$(if $(filter-out 1.0,$(compat_version)),"supported_devices": \
+			["$(call json_quote,Image version $(compat_version) incompatible to device: $(if $(DEVICE_COMPAT_MESSAGE),$(DEVICE_COMPAT_MESSAGE),Please check documentation ...)"]$(comma)) \
+		$(if $(filter 1.0,$(compat_version)),"supported_devices":[$(call metadata_devices,$(SUPPORTED_DEVICES))]$(comma)) \
 		"version": { \
 			"dist": "$(call json_quote,$(VERSION_DIST))", \
 			"version": "$(call json_quote,$(VERSION_NUMBER))", \
diff --git a/package/base-files/files/lib/upgrade/fwtool.sh b/package/base-files/files/lib/upgrade/fwtool.sh
index 1807aecd6d..59f981f6c3 100644
--- a/package/base-files/files/lib/upgrade/fwtool.sh
+++ b/package/base-files/files/lib/upgrade/fwtool.sh
@@ -51,7 +51,12 @@ fwtool_check_image() {
 	json_get_var compatmessage compat_message
 	[ -n "$imagecompat" ] || imagecompat="1.0"
 
-	json_select supported_devices || return 1
+	# select correct supported list based on compat_version
+	# (using this ensures that compatibility check works for devices
+	#  not knowing about compat-version)
+	local supported=supported_devices
+	[ "$imagecompat" != "1.0" ] && supported=new_supported_devices
+	json_select $supported || return 1
 
 	json_get_keys dev_keys
 	for k in $dev_keys; do
-- 
2.20.1