Merge changes from topic "snapuserd_ramdisk"

* changes:
  Prefer generic ramdisk copy of snapuserd
  Install snapuserd.ramdisk with a separate path

fs_mgr/libsnapshot/snapuserd/Android.bp

@@ -72,7 +72,7 @@ cc_defaults {
 
     cflags: [
         "-Wall",
-        "-Werror"
+        "-Werror",
     ],
 
     static_libs: [
@@ -89,14 +89,7 @@ cc_defaults {
         "liburing",
     ],
     include_dirs: ["bionic/libc/kernel"],
-}
+    system_shared_libs: [],
-
-cc_binary {
-    name: "snapuserd",
-    defaults: ["snapuserd_defaults"],
-    init_rc: [
-        "snapuserd.rc",
-    ],
 
     // snapuserd is started during early boot by first-stage init. At that
     // point, /system is mounted using the "dm-user" device-mapper kernel
@@ -105,16 +98,40 @@ cc_binary {
     // faults for its code pages.
     static_executable: true,
 
-    system_shared_libs: [],
-    ramdisk_available: true,
-    vendor_ramdisk_available: true,
-    recovery_available: true,
-
     // Snapuserd segfaults with ThinLTO
     // http://b/208565717
     lto: {
          never: true,
-    }
+    },
+}
+
+cc_binary {
+    name: "snapuserd",
+    defaults: ["snapuserd_defaults"],
+    init_rc: [
+        "snapuserd.rc",
+    ],
+    ramdisk_available: false,
+    vendor_ramdisk_available: true,
+    recovery_available: true,
+}
+
+// This target will install to /system/bin/snapuserd_ramdisk 
+// It will also create a symblink on /system/bin/snapuserd that point to
+// /system/bin/snapuserd_ramdisk .
+// This way, init can check if generic ramdisk copy exists.
+cc_binary {
+    name: "snapuserd_ramdisk",
+    defaults: ["snapuserd_defaults"],
+    init_rc: [
+        "snapuserd.rc",
+    ],
+    // This target is specifically for generic ramdisk, therefore we set
+    // vendor_ramdisk_available to false.
+    ramdisk_available: true,
+    vendor_ramdisk_available: false,
+    ramdisk: true,
+    symlinks: ["snapuserd"],
 }
 
 cc_test {

init/first_stage_init.cpp

@@ -119,19 +119,14 @@ static void Copy(const char* src, const char* dst) {
 // Move snapuserd before switching root, so that it is available at the same path
 // after switching root.
 void PrepareSwitchRoot() {
-    constexpr const char* src = "/system/bin/snapuserd";
+    static constexpr const auto& snapuserd = "/system/bin/snapuserd";
-    constexpr const char* dst = "/first_stage_ramdisk/system/bin/snapuserd";
+    static constexpr const auto& snapuserd_ramdisk = "/system/bin/snapuserd_ramdisk";
+    static constexpr const auto& dst = "/first_stage_ramdisk/system/bin/snapuserd";
 
     if (access(dst, X_OK) == 0) {
         LOG(INFO) << dst << " already exists and it can be executed";
         return;
     }
-
-    if (access(src, F_OK) != 0) {
-        PLOG(INFO) << "Not moving " << src << " because it cannot be accessed";
-        return;
-    }
-
     auto dst_dir = android::base::Dirname(dst);
     std::error_code ec;
     if (access(dst_dir.c_str(), F_OK) != 0) {
@@ -139,7 +134,18 @@ void PrepareSwitchRoot() {
             LOG(FATAL) << "Cannot create " << dst_dir << ": " << ec.message();
         }
     }
-    Copy(src, dst);
+
+    // prefer the generic ramdisk copy of snapuserd, because that's on system side of treble
+    // boundary, and therefore is more likely to be updated along with the Android platform.
+    // The vendor ramdisk copy might be under vendor freeze, or vendor might choose not to update
+    // it.
+    if (access(snapuserd_ramdisk, F_OK) == 0) {
+        LOG(INFO) << "Using generic ramdisk copy of snapuserd " << snapuserd_ramdisk;
+        Copy(snapuserd_ramdisk, dst);
+    } else if (access(snapuserd, F_OK) == 0) {
+        LOG(INFO) << "Using vendor ramdisk copy of snapuserd " << snapuserd;
+        Copy(snapuserd, dst);
+    }
 }
 }  // namespace