android 14 apexd分析（2）apexd 启动
1. class main进程一起启动， apexservice是他提供的binderservice，这也第二阶段的最主要的作用
/system/apex/apexd/apexd.rc?r=3c8e8603c640fc41e0406ddcf981381803447cfb#1
1 service apexd /system/bin/apexd
2 interface aidl apexservice ----------> aidl service
3 class core
4 user root
5 group system
6 oneshot
7 disabled # does not start with the core class
8 reboot_on_failure reboot,apexd-failed
9 # CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH required for apexdata snapshot & restore
10 # CAP_SYS_ADMIN is required to access device-mapper and to use mount syscall
11 capabilities CHOWN DAC_OVERRIDE DAC_READ_SEARCH FOWNER SYS_ADMIN
2. main()函数的的内容
/system/apex/apexd/apexd_main.cpp?r=3c8e8603c640fc41e0406ddcf981381803447cfb#106
106 int main(int /*argc*/, char** argv) {
.......
155 android::base::Result<android::apex::VoldCheckpointInterface>
156 vold_service_st = android::apex::VoldCheckpointInterface::Create(); ----> 获得Ivold binder service
157 android::apex::VoldCheckpointInterface* vold_service = nullptr;
158 if (!vold_service_st.ok()) {
159 LOG(ERROR) << "Could not retrieve vold service: "
160 << vold_service_st.error();
161 } else {
162 vold_service = &*vold_service_st;
163 }
164 android::apex::Initialize(vold_service); ----> 获得使用Ivold的一些初始化操作
165
166 if (booting) {
167 if (auto res = android::apex::MigrateSessionsDirIfNeeded(); !res.ok()) {
168 LOG(ERROR) << "Failed to migrate sessions to /metadata partition : "
169 << res.error();
170 }
171 android::apex::OnStart(); ----> onstart 这其中就会 decompress compressedapex 和 ActivateApexPackages()
172 } else {
173 // TODO(b/172911822): Trying to use data apex related ApexFileRepository
174 // apis without initializing it should throw error. Also, unit tests should
175 // not pass without initialization.
176 // TODO(b/172911822): Consolidate this with Initialize() when
177 // ApexFileRepository can act as cache and re-scanning is not expensive
178 android::apex::InitializeDataApex();
179 }
180 // start apexservice before ApexdLifecycle::WaitForBootStatus which waits for
181 // IApexService::markBootComplete().
182 android::apex::binder::CreateAndRegisterService(); ----> 把apexservice 添加到servicemanager中，这是个lazy service
183 android::apex::binder::StartThreadPool();
184
题外话:
想要使用apexservice命令时，需要加上-w参数，因为他是个lazyservice,-w 是start and wait的意思，调用的是sm->waitforservice这个方法:
Example:
cmd -w apexservice getAllPackages
cmd -w apexservice deactivatePackage /system/apex/com.android.virt.apex
cmd -w apexservice activatePackage /system/apex/com.android.virt.apexcompressed apex解压如下:(实际上是对origin_apex又包了一层)
com.google.android.art_compressed$ ls
AndroidManifest.xml apex_build_info.pb apex_manifest.pb apex_pubkey META-INF original_apex original stamp-cert-sha256
com.google.android.art_compressed/original_apex $ ls
AndroidManifest.xml apex_build_info.pb apex_manifest.pb apex_payload.img apex_pubkey assets META-INF stamp-cert-sha256
3.ProcessCompressedApex() 把compressed apex搞到/data/apex/decompressed/下面
其中有一个验证比较有意思拉出来单聊，其他我也没兴趣，就没细看
2990 Result<void> ValidateDecompressedApex(const ApexFile& capex,
2991 const ApexFile& apex) {
2992 // Decompressed APEX must have same public key as CAPEX
2993 if (capex.GetBundledPublicKey() != apex.GetBundledPublicKey()) {=========> 1 压缩包的apexpubkey和original_apex的aepxpubkey是一样的
2994 return Error()
2995 << "Public key of compressed APEX is different than original "
2996 << "APEX for " << apex.GetPath();
2997 }
2998 // Decompressed APEX must have same version as CAPEX 2 ======>压缩包的version和original_apex的version是一样的
2999 if (capex.GetManifest().version() != apex.GetManifest().version()) {
3000 return Error()
3001 << "Compressed APEX has different version than decompressed APEX "
3002 << apex.GetPath();
3003 }
3004 // Decompressed APEX must have same root digest as what is stored in CAPEX
3005 auto apex_verity = apex.VerifyApexVerity(apex.GetBundledPublicKey()); =======> 3 首先验证decompressed apex自己的avb特性
3006 if (!apex_verity.ok() ||
3007 capex.GetManifest().capexmetadata().originalapexdigest() !=
3008 apex_verity->root_digest) {
3009 return Error() << "Root digest of " << apex.GetPath() =======> 4 再和compressed apex的manifest的root digest对比一下，见CompressedApexMetadata
3010 << " does not match with"
3011 << " expected root digest in " << capex.GetPath();
3012 }
3013 return {};
3014 }秘钥的结果一模一样，就问你牛不牛逼
python3 avbtool.py info_image --image apex_payload.img
Footer version: 1.0
Image size: 831488 bytes
Original image size: 811008 bytes
VBMeta offset: 823296
VBMeta size: 2240 bytes
--
Minimum libavb version: 1.0
Header Block: 256 bytes
Authentication Block: 576 bytes
Auxiliary Block: 1408 bytes
Public key (sha1): 184474f2094c5dcbfc923af813bebddbf3f712e8
Algorithm: SHA256_RSA4096
Rollback Index: 0
Flags: 0
Rollback Index Location: 0
Release String: 'avbtool 1.2.0'
Descriptors:Hashtree descriptor: ------------------------------------- apex 用的是hashtreeVersion of dm-verity: 1Image Size: 811008 bytes -----> 198 blocksTree Offset: 811008Tree Size: 12288 bytes ------> 3 blocksData Block Size: 4096 bytesHash Block Size: 4096 bytesFEC num roots: 0FEC offset: 0FEC size: 0 bytesHash Algorithm: sha256Partition Name: Salt: b1c8aab92b646d2d85d0553fa1d3e0bea4c7289e2b740ae6079d40a490631bc0Root Digest: 25aaef0ecde6d8d66458d20f8ff4ef808c2630410443ffec18d82d8647aa332aFlags: 0Prop: apex.key -> 'com_google_android_ipsec-image' $ cat ./apex_pubkey |sha1sum
184474f2094c5dcbfc923af813bebddbf3f712e8hashtree的size的计算从layer 1开始，所以是3 blocks, 对于sha256算法，128个data block对应一个hashtree blocklayer 2 root_hash_blk0/ \
layer 1 hash_blk_0 hash_blk_1/ \ / \
layer 0 [blk_0] ....[blk_127] [blk_128]....[blk_197]
4. ActivateApexPackages() 同上一章
5.PMS和apex的联系,用adb install apex
PMS在安装apex的时候，其实是通过apexservice 调用apexservice的
installAndActivatePackage()方法
/frameworks/base/services/core/java/com/android/server/pm/InstallingSession.java?r=3491936bce332909e2b20f7891ced303b9806925#495
495 private void processInstallRequests(boolean success, List<InstallRequest> installRequests) {
496 List<InstallRequest> apexInstallRequests = new ArrayList<>();
497 List<InstallRequest> apkInstallRequests = new ArrayList<>();
498 for (InstallRequest request : installRequests) {
499 if ((request.getInstallFlags() & PackageManager.INSTALL_APEX) != 0) {
500 apexInstallRequests.add(request);
501 } else {
502 apkInstallRequests.add(request);
503 }
504 }
505 // Note: supporting multi package install of both APEXes and APKs might requir some
506 // thinking to ensure atomicity of the install.
507 if (!apexInstallRequests.isEmpty() && !apkInstallRequests.isEmpty()) {
508 // This should've been caught at the validation step, but for some reason wasn't.
509 throw new IllegalStateException(
510 "Attempted to do a multi package install of both APEXes and APKs");
511 }
512 if (!apexInstallRequests.isEmpty()) {
513 if (success) {
514 // Since installApexPackages requires talking to external service (apexd), we
515 // schedule to run it async. Once it finishes, it will resume the install.
516 Thread t = new Thread(() -> installApexPackagesTraced(apexInstallRequests), ====> 其实是调用的installAndActivatePackage()
517 "installApexPackages");
518 t.start();
519 } else {
520 // Non-staged APEX installation failed somewhere before
521 // processInstallRequestAsync. In that case just notify the observer about the
522 // failure.
523 InstallRequest request = apexInstallRequests.get(0);
524 mPm.notifyInstallObserver(request);
525 }
526 return;
527 }
528
529 processApkInstallRequests(success, installRequests); ====> 普通apk的安装
530 }adb install apex命令和结果:
$ adb install com.android.ipsec@340818020.decompressed.apex
Performing Streamed Install
Success. Reboot device to apply staged session