health 1.0: add helper library for -impl

Now that libhealthd is no longer recognized as a HAL_STATIC_LIBRARY,
vendors must define their own android.hardware.health@1.0-impl module.
Add a helper and README.md for them to explain this transition.

Test: builds
Bug: 127677771
Change-Id: I65c162e7b5caed93c39a4a1cb6a2893fbb25724b

health/1.0/default/Android.bp

@@ -18,10 +18,9 @@ cc_library_static {
 
 }
 
-cc_library_shared {
-    name: "android.hardware.health@1.0-impl",
+cc_library_static {
+    name: "android.hardware.health@1.0-impl-helper",
     vendor: true,
-    relative_install_path: "hw",
     srcs: ["Health.cpp"],
 
     header_libs: [
@@ -39,6 +38,17 @@ cc_library_shared {
 
     static_libs: [
         "android.hardware.health@1.0-convert",
+    ],
+}
+
+cc_library_shared {
+    name: "android.hardware.health@1.0-impl",
+    vendor: true,
+    relative_install_path: "hw",
+
+    static_libs: [
+        "android.hardware.health@1.0-impl-helper",
+        "android.hardware.health@1.0-convert",
         "libhealthd.default",
     ],
 }

health/1.0/default/README.md

@@ -0,0 +1,66 @@
+# Implement the 2.1 HAL instead!
+
+It is strongly recommended that you implement the 2.1 HAL directly. See
+`hardware/interfaces/health/2.1/README.md` for more details.
+
+# Implement Health 1.0 HAL
+
+1. Install common binderized service. The binderized service `dlopen()`s
+   passthrough implementations on the device, so there is no need to write
+   your own.
+
+    ```mk
+    # Install default binderized implementation to vendor.
+    PRODUCT_PACKAGES += android.hardware.health@1.0-service
+    ```
+
+1. Add proper VINTF manifest entry to your device manifest. Example:
+
+    ```xml
+    <hal format="hidl">
+        <name>android.hardware.health</name>
+        <transport>hwbinder</transport>
+        <version>1.0</version>
+        <interface>
+            <name>IHealth</name>
+            <instance>default</instance>
+        </interface>
+    </hal>
+    ```
+
+1. Install the proper passthrough implemetation.
+
+    1. If you want to use the default implementation (with default `libhealthd`),
+       add the following to `device.mk`:
+
+        ```mk
+        PRODUCT_PACKAGES += \
+            android.hardware.health@1.0-impl
+        ```
+
+    1. Otherwise, if you have a customized `libhealthd.<board>`:
+
+        1. Define your passthrough implementation. Example (replace `<device>`
+           and `<board>` accordingly):
+
+            ```bp
+            cc_library_shared {
+                name: "android.hardware.health@1.0-impl-<device>",
+                vendor: true,
+                relative_install_path: "hw",
+
+                static_libs: [
+                    "android.hardware.health@1.0-impl-helper",
+                    "android.hardware.health@1.0-convert",
+                    "libhealthd.<board>",
+                ],
+            }
+            ```
+
+        1. Add to `device.mk`.
+
+            ```
+            PRODUCT_PACKAGES += android.hardware.health@1.0-impl-<device>
+            ```
+
+        1. Define appropriate SELinux permissions.