[OpenWrt-Devel] [RFC PATCH] sysupgrade: introduce compatibility version for devices

[Adrian Schmutzler]

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 patch introduces a compatibility
version for devices. It will be implemented via a per-device
Make variable DEVICE_COMPAT_VERSION, which will be set to 1.0
globally by default and then can be overwritten as needed.
The value for "old" devices/images without it is assumed to be
1.0 as well.

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

The former will still allow sysupgrade and only require to have
-n set to wipe existing config. The latter is meant for cases
where sysupgrade will break entirely, and a new installation should
be performed. Both can still be forced as usual (-F).

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

---

** HELP NEEDED **

This patch is completely untested and won't work right now due to the
following problem:

The major obstacle (not implemented at all) currently is how to
get the compat version (on)to the running device. Including it into
image metadata is easy, but how to properly transform the Make
variable into a variable on the device? (Of course, I can just
create a separate file and write to it, but maybe there are
better ways I don't see right now.)

Of course, the current draft will only work after the second upgrade,
i.e. when upgrading from the new firmware to an even newer one.
I'm currently trying to work around that and provide compatibility
with older images as well, e.g. by renaming the supported_devices
in metadata based on the compat_version.
---
 include/image-commands.mk                      |  5 +++--
 include/image.mk                               |  3 ++-
 package/base-files/files/lib/upgrade/fwtool.sh | 17 +++++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/image-commands.mk b/include/image-commands.mk
index e7db7128b4..53ee24aa36 100644
--- a/include/image-commands.mk
+++ b/include/image-commands.mk
@@ -390,7 +390,8 @@ metadata_devices=$(if $(1),$(subst "$(space)","$(comma)",$(strip $(foreach v,$(1
 metadata_json = \
 	'{ $(if $(IMAGE_METADATA),$(IMAGE_METADATA)$(comma)) \
 		"metadata_version": "1.0", \
-		"supported_devices":[$(call metadata_devices,$(1))], \
+		"compat_version": "$(call json_quote,$(if $(DEVICE_COMPAT_VERSION),$(DEVICE_COMPAT_VERSION),1.0))", \
+		"supported_devices":[$(call metadata_devices,$(SUPPORTED_DEVICES))], \
 		"version": { \
 			"dist": "$(call json_quote,$(VERSION_DIST))", \
 			"version": "$(call json_quote,$(VERSION_NUMBER))", \
@@ -401,7 +402,7 @@ metadata_json = \
 	}'
 
 define Build/append-metadata
-	$(if $(SUPPORTED_DEVICES),-echo $(call metadata_json,$(SUPPORTED_DEVICES)) | fwtool -I - $@)
+	$(if $(SUPPORTED_DEVICES),-echo $(call metadata_json) | fwtool -I - $@)
 	[ ! -s "$(BUILD_KEY)" -o ! -s "$(BUILD_KEY).ucert" -o ! -s "$@" ] || { \
 		cp "$(BUILD_KEY).ucert" "$@.ucert" ;\
 		usign -S -m "$@" -s "$(BUILD_KEY)" -x "$@.sig" ;\
diff --git a/include/image.mk b/include/image.mk
index 984b64fb9c..346ab0d5d3 100644
--- a/include/image.mk
+++ b/include/image.mk
@@ -419,6 +419,7 @@ define Device/Init
 
   BOARD_NAME :=
   UIMAGE_NAME :=
+  DEVICE_COMPAT_VERSION := 1.0
   SUPPORTED_DEVICES :=
   IMAGE_METADATA :=
 
@@ -435,7 +436,7 @@ DEFAULT_DEVICE_VARS := \
   VID_HDR_OFFSET UBINIZE_OPTS UBINIZE_PARTS MKUBIFS_OPTS DEVICE_DTS \
   DEVICE_DTS_CONFIG DEVICE_DTS_DIR SOC BOARD_NAME UIMAGE_NAME SUPPORTED_DEVICES \
   IMAGE_METADATA KERNEL_ENTRY KERNEL_LOADADDR UBOOT_PATH IMAGE_SIZE \
-  DEVICE_VENDOR DEVICE_MODEL DEVICE_VARIANT \
+  DEVICE_COMPAT_VERSION DEVICE_VENDOR DEVICE_MODEL DEVICE_VARIANT \
   DEVICE_ALT0_VENDOR DEVICE_ALT0_MODEL DEVICE_ALT0_VARIANT \
   DEVICE_ALT1_VENDOR DEVICE_ALT1_MODEL DEVICE_ALT1_VARIANT \
   DEVICE_ALT2_VENDOR DEVICE_ALT2_MODEL DEVICE_ALT2_VARIANT
diff --git a/package/base-files/files/lib/upgrade/fwtool.sh b/package/base-files/files/lib/upgrade/fwtool.sh
index a0b3fb0a04..b887408f7e 100644
--- a/package/base-files/files/lib/upgrade/fwtool.sh
+++ b/package/base-files/files/lib/upgrade/fwtool.sh
@@ -44,6 +44,23 @@ fwtool_check_image() {
 	}
 
 	device="$(cat /tmp/sysinfo/board_name)"
+	compat="$(cat somewherelocal)"
+	[ -n "$compat" ] || compat="1.0"
+
+	json_get_var imagecompat compat_version
+	[ -n "$imagecompat" ] || imagecompat="1.0"
+
+	# major compat version -> no sysupgrade
+	if [ "${compat%.*}" != "${imagecompat%.*}" ]; then
+		echo "This image is incompatible for sysupgrading based on the image version."
+		return 1
+	fi
+
+	# minor compat version -> sysupgrade with -n required
+	if [ "${compat#.*}" != "${imagecompat#.*}" ] && [ "$SAVE_CONFIG" = "1" ]; then
+		echo "This config is incompatible to the new image. Please upgrade with -n"
+		return 1
+	fi
 
 	json_select supported_devices || return 1
 
-- 
2.20.1


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