There are two kinds of Android upgrades, one is to upgrade a single file in the system, the other is to upgrade the entire partition of mtd, and the upgrade package is a signature compressed file compressed into zip format. The main flow of the upgrade process is described as follows: 1boot found that the user pressed the upgrade button and read recovery.img into memory as ramdisk. The kernel executes the recovery script according to init.rc in ramdisk. After the recovery script finds the upgrade file in sdcard, it calls the recovery program to do the following operations in turn: a Check whether the digital signature of the upgrade file is reliable. The local key used to check the signature is /res/keys. B if the signature is legal, extract the meta-INF/com/Google/Android/update-binary file from the compressed package, rename it to /tmp/update_binary and execute the file. Cupdate_binary parses the meta-INF/com/Google/Android/updater-script file in the compressed file and executes it. The upgrade progress is sent back to the recovery program through the pipeline. The upgrade/update can directly overwrite the target file or take the form of binary patch to reduce the capacity of the upgraded file. The tools used are bsdiff and imgdiff. For the upgrade form of patch package, the reliability identification of upgrade data source is based on sha 1 checksum and data length comparison. The specific requirement is that the Sha 1 value of the target file provided by the1upgrade package is consistent with the calculated value of the target file, that is, the target is correct. The sha 1 value and length of the patch file are consistent with the length and sha 1 value of the patch target file provided by the upgrade package to ensure the correct result. If one of the two items does not match, the upgrade process will stop. In order to ensure that the second operation will not destroy the final target, the patched file will be temporarily stored in the cache until the result is correct before the actual writing/replacement operation of the target file. Therefore, this process requires that the cache directory must have enough space to save temporary files. Quote "working doctor _ _".