add android_filesystem

android_filesystem is a module type that can be used to create filesystem
images out of binaries built for Android. Its initial use will be for
creating an Android-like OS image to run on virtual machines, but the
use is not limited to it.

The module type currently lacks a lot of features like the support for
other filesystem types, and the ability to do something like signing the
image using avbtool, etc. Those will be added in follow-up CLs as we
have actual demands.

Bug: 172414391
Test: m
Change-Id: I4b779d4586e04d9a960688e73b711166708558ab

filesystem/Android.bp

@@ -0,0 +1,15 @@
+bootstrap_go_package {
+    name: "soong-filesystem",
+    pkgPath: "android/soong/filesystem",
+    deps: [
+        "blueprint",
+        "soong",
+        "soong-android",
+    ],
+    srcs: [
+        "filesystem.go",
+    ],
+    testSrcs: [
+    ],
+    pluginFor: ["soong_build"],
+}

filesystem/filesystem.go

@@ -0,0 +1,76 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package filesystem
+
+import (
+	"fmt"
+
+	"android/soong/android"
+)
+
+func init() {
+	android.RegisterModuleType("android_filesystem", filesystemFactory)
+}
+
+type filesystem struct {
+	android.ModuleBase
+	android.PackagingBase
+}
+
+func filesystemFactory() android.Module {
+	module := &filesystem{}
+	android.InitPackageModule(module)
+	android.InitAndroidMultiTargetsArchModule(module, android.DeviceSupported, android.MultilibCommon)
+	return module
+}
+
+func (f *filesystem) DepsMutator(ctx android.BottomUpMutatorContext) {
+	f.AddDeps(ctx)
+}
+
+var pctx = android.NewPackageContext("android/soong/filesystem")
+
+func (f *filesystem) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	zipFile := android.PathForModuleOut(ctx, "temp.zip").OutputPath
+	f.CopyDepsToZip(ctx, zipFile)
+
+	rootDir := android.PathForModuleOut(ctx, "root").OutputPath
+	builder := android.NewRuleBuilder()
+	builder.Command().
+		BuiltTool(ctx, "zipsync").
+		FlagWithArg("-d ", rootDir.String()). // zipsync wipes this. No need to clear.
+		Input(zipFile)
+
+	mkuserimg := ctx.Config().HostToolPath(ctx, "mkuserimg_mke2fs")
+	propFile := android.PathForModuleOut(ctx, "prop").OutputPath
+	// TODO(jiyong): support more filesystem types other than ext4
+	propsText := fmt.Sprintf(`mount_point=system\n`+
+		`fs_type=ext4\n`+
+		`use_dynamic_partition_size=true\n`+
+		`ext_mkuserimg=%s\n`, mkuserimg.String())
+	builder.Command().Text("echo").Flag("-e").Flag(`"` + propsText + `"`).
+		Text(">").Output(propFile).
+		Implicit(mkuserimg)
+
+	image := android.PathForModuleOut(ctx, "filesystem.img").OutputPath
+	builder.Command().BuiltTool(ctx, "build_image").
+		Text(rootDir.String()). // input directory
+		Input(propFile).
+		Output(image).
+		Text(rootDir.String()) // directory where to find fs_config_files|dirs
+
+	// rootDir is not deleted. Might be useful for quick inspection.
+	builder.Build(pctx, ctx, "build_filesystem_image", fmt.Sprintf("Creating filesystem %s", f.BaseModuleName()))
+}