前言
在 Android HIDL 详解 一文提到HIDL 使用的整个过程都是跟其工具hidl-gen 分不开，这一篇来详细分析hidl-gen 的使用。
代码基于：Android P
使用
hidl-gen 的代码路径为：system/tools/hidl
cc_library_host_shared {
name: "libhidl-gen",
defaults: ["hidl-gen-defaults"],
srcs: [
"Annotation.cpp",
"ArrayType.cpp",
"CompoundType.cpp",
"ConstantExpression.cpp",
"DeathRecipientType.cpp",
"DocComment.cpp",
"EnumType.cpp",
"HandleType.cpp",
"HidlTypeAssertion.cpp",
...
编译之后会在out 下生成，详细看out/host/linux-x86/bin/hidl-gen
编译好之后可以通过详细路径直接使用，也可以设置环境变量、lunch之后使用：
shift:shift# hidl-gen -h
usage: hidl-gen [-p <root path>] -o <output path> -L <language> [-O <owner>] (-r <interface root>)+ [-v] [-d <depfile>] FQNAME...
Process FQNAME, PACKAGE(.SUBPACKAGE)*@[0-9]+.[0-9]+(::TYPE)?, to create output.
-h: Prints this menu.
-L <language>: The following options are available:
check : Parses the interface to see if valid but doesn't write any files.
c++ : (internal) (deprecated) Generates C++ interface files for talking to HIDL interfaces.
c++-headers : (internal) Generates C++ headers for interface files for talking to HIDL interfaces.
c++-sources : (internal) Generates C++ sources for interface files for talking to HIDL interfaces.
export-header : Generates a header file from @export enumerations to help maintain legacy code.
c++-impl : Generates boilerplate implementation of a hidl interface in C++ (for convenience).
c++-impl-headers: c++-impl but headers only
c++-impl-sources: c++-impl but sources only
c++-adapter : Takes a x.(y+n) interface and mocks an x.y interface.
c++-adapter-headers: c++-adapter but helper headers only
c++-adapter-sources: c++-adapter but helper sources only
c++-adapter-main: c++-adapter but the adapter binary source only
java : (internal) Generates Java library for talking to HIDL interfaces in Java.
java-constants : (internal) Like export-header but for Java (always created by -Lmakefile if @export exists).
vts : (internal) Generates vts proto files for use in vtsd.
makefile : (removed) Used to generate makefiles for -Ljava and -Ljava-constants.
androidbp : (internal) Generates Soong bp files for -Lc++-headers, -Lc++-sources, -Ljava, -Ljava-constants, and -Lc++-adapter.
androidbp-impl : Generates boilerplate bp files for implementation created with -Lc++-impl.
hash : Prints hashes of interface in `current.txt` format to standard out.
-O <owner>: The owner of the module for -Landroidbp(-impl)?.
-o <output path>: Location to output files.
-p <root path>: Android build root, defaults to $ANDROID_BUILD_TOP or pwd.
-r <package:path root>: E.g., android.hardware:hardware/interfaces.
-v: verbose output.
-d <depfile>: location of depfile to write to.
在创建对应模块的hal 文件之后，通过hidl-gen 就可以简单的创建一些开发的文件。
update-makefiles.sh
通过/hardware/interfaces/update-makefiles.sh 可以创建编译HIDL 文件的Android.bp。
假设我们创建一个helloworld的模块，在hardware/interfaces 下创建helloworld/1.0/IHelloWorld.hal：
package android.hardware.helloworld@1.0;
interface IHelloWorld {
justTest(string name);
};
通过update-makefiles.sh 就可以在对应package 的目录下创建Android.bp：
// This file is autogenerated by hidl-gen -Landroidbp.
hidl_interface {
name: "android.hardware.helloworld@1.0",
root: "android.hardware",
vndk: {
enabled: true,
},
srcs: [
"IHelloWorld.hal",
],
interfaces: [
"android.hidl.base@1.0",
],
gen_java: true,
}
name：FQName 的全名
root：定义好的package root name，详细看Android HIDL 接口和软件包使用
interfaces：编译过程中依赖的接口名称，如c 中的shared library
gen_java：是否编译为Java 使用的接口
当然，还有其他的参数，例如gen_java_constants设为true 的时候会生成为Java 使用的Constants类。
可以根据实际情况修改该Android.bp
update-files.sh
IHelloWorld.hal 和对应的Android.bp 创建好后，就可以根据需要实现FQName-impl 和FQName-service所需要的文件，而这些文件也是通过hidl-gen 创建的，就是下面这个脚本。
#! /bin/bash
PACKAGE=android.hardware.helloworld@1.0
LOC=hardware/interfaces/helloworld/1.0/default/
hidl-gen -o $LOC -Lc++-impl -randroid.hardware:hardware/interfaces \
-randroid.hidl:system/libhidl/transport $PACKAGE
hidl-gen -o $LOC -Landroidbp-impl -randroid.hardware:hardware/interfaces \
-randroid.hidl:system/libhidl/transport $PACKAGE
可以看到创建的是c++-impl 所需要的文件以及对应的Android.bp。执行后如下：
~/work/LA.UM.7.6/LINUX/android/hardware/interfaces/helloworld/1.0/default:
ll
total 20
drwxr-xr-x 2 shift shift 4096 1月 17 20:05 ./
drwxrwxr-x 3 shift shift 4096 1月 17 20:05 ../
-rw-rw-r-- 1 shift shift 973 1月 17 20:05 Android.bp
-rw-rw-r-- 1 shift shift 605 1月 17 20:05 HelloWorld.cpp
-rw-rw-r-- 1 shift shift 1159 1月 17 20:05 HelloWorld.h
创建后的Android.bp如下：
cc_library_shared {
// FIXME: this should only be -impl for a passthrough hal.
// In most cases, to convert this to a binderized implementation, you should:
// - change '-impl' to '-service' here and make it a cc_binary instead of a
// cc_library_shared.
// - add a *.rc file for this module.
// - delete HIDL_FETCH_I* functions.
// - call configureRpcThreadpool and registerAsService on the instance.
// You may also want to append '-impl/-service' with a specific identifier like
// '-vendor' or '-<hardware identifier>' etc to distinguish it.
name: "android.hardware.helloworld@1.0-impl",
relative_install_path: "hw",
// FIXME: this should be 'vendor: true' for modules that will eventually be
// on AOSP.
proprietary: true,
srcs: [
"HelloWorld.cpp",
],
shared_libs: [
"libhidlbase",
"libhidltransport",
"libutils",
"android.hardware.helloworld@1.0",
],
}
如注释部分，可以根据特殊的需要进行修改，例如，vendor 需要设为true，这样编译出来的so位于vendor下面，而不是system。也可以使用同样的方式为FQName-service 创建对应的规则。
关于HIDL 在helloworld的详细使用可以看另一篇博文：Android HIDL 实例
相关文章：
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Android HIDL 详解
Android HIDL 编程规范
Android HIDL 接口和软件包使用
Android HIDL 实例
Android HIDL 中的函数
Android HIDL 中的数据类型
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