From 2e1ade925cf9970b1f764676a3abcc835088d83b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?M=C3=A5rten=20Kongstad?= Date: Fri, 31 Jan 2014 14:43:49 +0100 Subject: [PATCH] Runtime resource overlay, iteration 2 Support any number of overlay packages. Support any target package. UPDATED PACKAGE MATCHING ------------------------ In Runtime resource overlay, iteration 1, only a single overlay package was considered. Package matching was based on file paths: /vendor/overlay/system/framework-res.apk corresponded to /system/framework-res.apk. Introduce a more flexible matching scheme where any package is an overlay package if its manifest includes For security reasons, an overlay package must fulfill certain criteria to take effect: see below. THE IDMAP TOOL AND IDMAP FILES ------------------------------ Idmap files are created by the 'idmap' binary; idmap files must be present when loading packages. For the Android system, Zygote calls 'idmap' as part of the resource pre-loading. For application packages, 'idmap' is invoked via 'installd' during package installation (similar to 'dexopt'). UPDATED FLOW ------------ The following is an outline of the start-up sequences for the Android system and Android apps. Steps marked with '+' are introduced by this commit. Zygote initialization Initial AssetManager object created + idmap --scan creates idmaps for overlays targeting 'android', \ stores list of overlays in /data/resource-cache/overlays.list AssetManager caches framework-res.apk + AssetManager caches overlay packages listed in overlays.list Android boot New AssetManager's ResTable acquired AssetManager re-uses cached framework-res.apk + AssetManager re-uses cached 'android' overlays (if any) App boot ActivityThread prepares AssetManager to load app.apk + ActivityThread prepares AssetManager to load app overlays (if any) New AssetManager's ResTable acquired as per Android boot SECURITY -------- Overlay packages are required to be pre-loaded (in /vendor/overlay). These packages are trusted by definition. A future iteration of runtime resource overlay may add support for downloaded overlays, which would likely require target and overlay signatures match for the overlay to be trusted. LOOKUP PRIORITY --------------- During resource lookup, packages are sequentially queried to provide a best match, given the constraints of the current configuration. If any package provide a better match than what has been found so far, it replaces the previous match. The target package is always queried last. When loading a package with more than one overlay, the order in which the overlays are added become significant if several packages overlay the same resource. Had downloaded overlays been supported, the install time could have been used to determine the load order. Regardless, for pre-installed overlays, the install time is randomly determined by the order in which the Package Manager locates the packages during initial boot. To support a well-defined order, pre-installed overlay packages are expected to define an additional 'priority' attribute in their tags: Pre-installed overlays are loaded in order of their priority attributes, sorted in ascending order. Assigning the same priority to several overlays targeting the same base package leads to undefined behaviour. It is the responsibility of the vendor to avoid this. The following example shows the ResTable and PackageGroups after loading an application and two overlays. The resource lookup framework will query the packages in the order C, B, A. +------+------+- -+------+------+ | 0x01 | | ... | | 0x7f | +------+------+- -+------+------+ | | "android" Target package A | Pre-installed overlay B (priority 1) | Pre-installed overlay C (priority 2) Change-Id: If49c963149369b1957f7d2303b3dd27f669ed24e --- target/product/core_minimal.mk | 1 + 1 file changed, 1 insertion(+) diff --git a/target/product/core_minimal.mk b/target/product/core_minimal.mk index 79ba0d490..17000acde 100644 --- a/target/product/core_minimal.mk +++ b/target/product/core_minimal.mk @@ -37,6 +37,7 @@ PRODUCT_PACKAGES += \ com.android.media.remotedisplay.xml \ drmserver \ framework-res \ + idmap \ installd \ ip \ ip-up-vpn \