[avb_footer] Add avb_gen_vbmeta_image to generate vbmeta image

Bug: 260821553
Test: m microdroid_kernel_signed and inspect the output using `avbtool
    info_image --image <output>`
Change-Id: Iacdf34aca15f5480766b6d4f971704f85f6bf44b

filesystem/avb_gen_vbmeta_image.go

@@ -0,0 +1,108 @@
+// Copyright (C) 2022 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"
+
+	"github.com/google/blueprint/proptools"
+
+	"android/soong/android"
+)
+
+type avbGenVbmetaImage struct {
+	android.ModuleBase
+
+	properties avbGenVbmetaImageProperties
+
+	output     android.OutputPath
+	installDir android.InstallPath
+}
+
+type avbGenVbmetaImageProperties struct {
+	// Source file of this image. Can reference a genrule type module with the ":module" syntax.
+	Src *string `android:"path,arch_variant"`
+
+	// Name of the image partition. Defaults to the name of this module.
+	Partition_name *string
+
+	// The salt in hex. Required for reproducible builds.
+	Salt *string
+}
+
+// The avbGenVbmetaImage generates an unsigned VBMeta image output for the given image.
+func avbGenVbmetaImageFactory() android.Module {
+	module := &avbGenVbmetaImage{}
+	module.AddProperties(&module.properties)
+	android.InitAndroidArchModule(module, android.DeviceSupported, android.MultilibFirst)
+	return module
+}
+
+func (a *avbGenVbmetaImage) installFileName() string {
+	return a.Name() + ".img"
+}
+
+func (a *avbGenVbmetaImage) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	builder := android.NewRuleBuilder(pctx, ctx)
+	cmd := builder.Command().BuiltTool("avbtool").Text("add_hash_footer")
+	cmd.Flag("--dynamic_partition_size")
+	cmd.Flag("--do_not_append_vbmeta_image")
+
+	partition_name := proptools.StringDefault(a.properties.Partition_name, a.Name())
+	cmd.FlagWithArg("--partition_name ", partition_name)
+
+	if a.properties.Src == nil {
+		ctx.PropertyErrorf("src", "missing source file")
+		return
+	}
+	input := android.PathForModuleSrc(ctx, proptools.String(a.properties.Src))
+	cmd.FlagWithInput("--image ", input)
+
+	if a.properties.Salt == nil {
+		ctx.PropertyErrorf("salt", "missing salt value")
+		return
+	}
+	cmd.FlagWithArg("--salt ", proptools.String(a.properties.Salt))
+
+	a.output = android.PathForModuleOut(ctx, a.installFileName()).OutputPath
+	cmd.FlagWithOutput("--output_vbmeta_image ", a.output)
+	builder.Build("avbGenVbmetaImage", fmt.Sprintf("avbGenVbmetaImage %s", ctx.ModuleName()))
+}
+
+var _ android.AndroidMkEntriesProvider = (*avbGenVbmetaImage)(nil)
+
+// Implements android.AndroidMkEntriesProvider
+func (a *avbGenVbmetaImage) AndroidMkEntries() []android.AndroidMkEntries {
+	return []android.AndroidMkEntries{android.AndroidMkEntries{
+		Class:      "ETC",
+		OutputFile: android.OptionalPathForPath(a.output),
+		ExtraEntries: []android.AndroidMkExtraEntriesFunc{
+			func(ctx android.AndroidMkExtraEntriesContext, entries *android.AndroidMkEntries) {
+				entries.SetString("LOCAL_MODULE_PATH", a.installDir.String())
+				entries.SetString("LOCAL_INSTALLED_MODULE_STEM", a.installFileName())
+			},
+		},
+	}}
+}
+
+var _ android.OutputFileProducer = (*avbGenVbmetaImage)(nil)
+
+// Implements android.OutputFileProducer
+func (a *avbGenVbmetaImage) OutputFiles(tag string) (android.Paths, error) {
+	if tag == "" {
+		return []android.Path{a.output}, nil
+	}
+	return nil, fmt.Errorf("unsupported module reference tag %q", tag)
+}