Set libavb version into system property for Treble OTA

Set ro.boot.avb_version to "AVB_VERSION_MAJOR.AVB_VERSION_MINOR".
During Treble OTA match, the major version must be the same as that in
the avb metadata on disk, while the minor version can be equal or
greater to that in the avb metadata on disk.

See how avb versioning work on the following link:

  https://android-review.googlesource.com/#/c/342757/

Also renames AvbHashtreeDisabled() -> hashtree_disabled().

Bug: 35322304
Test: Early mount with AVB, checks [ro.boot.avb_version]: [1.0] exists.
Test: Not enable AVB, checks [ro.boot.avb_version] doesn't exists.

Change-Id: I5aaf476ca53c4fe817779518ba14b68ebcfdc6d6
diff --git a/fs_mgr/fs_mgr_avb.cpp b/fs_mgr/fs_mgr_avb.cpp
index 7c82bb1..83bf8a7 100644
--- a/fs_mgr/fs_mgr_avb.cpp
+++ b/fs_mgr/fs_mgr_avb.cpp
@@ -493,6 +493,10 @@
         return nullptr;
     }
 
+    // Sets the MAJOR.MINOR for init to set it into "ro.boot.avb_version".
+    avb_handle->avb_version_ =
+        android::base::StringPrintf("%d.%d", AVB_VERSION_MAJOR, AVB_VERSION_MINOR);
+
     // Verifies vbmeta images against the digest passed from bootloader.
     if (!avb_verifier->VerifyVbmetaImages(*avb_handle->avb_slot_data_)) {
         LERROR << "VerifyVbmetaImages failed";
diff --git a/fs_mgr/include/fs_mgr_avb.h b/fs_mgr/include/fs_mgr_avb.h
index 526a5ce..a66ff42 100644
--- a/fs_mgr/include/fs_mgr_avb.h
+++ b/fs_mgr/include/fs_mgr_avb.h
@@ -72,7 +72,8 @@
     // Otherwise, returns false.
     bool SetUpAvb(fstab_rec* fstab_entry, bool wait_for_verity_dev);
 
-    bool AvbHashtreeDisabled() { return status_ == kFsManagerAvbHandleHashtreeDisabled; }
+    bool hashtree_disabled() const { return status_ == kFsManagerAvbHandleHashtreeDisabled; }
+    const std::string& avb_version() const { return avb_version_; }
 
     FsManagerAvbHandle(const FsManagerAvbHandle&) = delete;             // no copy
     FsManagerAvbHandle& operator=(const FsManagerAvbHandle&) = delete;  // no assignment
@@ -92,6 +93,7 @@
   private:
     AvbSlotVerifyData* avb_slot_data_;
     FsManagerAvbHandleStatus status_;
+    std::string avb_version_;
 };
 
 #endif /* __CORE_FS_MGR_AVB_H */
diff --git a/init/init.cpp b/init/init.cpp
index 6c1c541..181b18d 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -1010,10 +1010,11 @@
         return false;
     }
 
+    setenv("INIT_AVB_VERSION", avb_handle->avb_version().c_str(), 1);
     for (auto rec : fstab_recs) {
         bool need_create_dm_device = false;
         if (fs_mgr_is_avb(rec)) {
-            if (avb_handle->AvbHashtreeDisabled()) {
+            if (avb_handle->hashtree_disabled()) {
                 LOG(INFO) << "avb hashtree disabled for '" << rec->mount_point << "'";
             } else if (avb_handle->SetUpAvb(rec, false /* wait_for_verity_dev */)) {
                 need_create_dm_device = true;
@@ -1362,12 +1363,14 @@
     property_set("ro.boottime.init.selinux", getenv("INIT_SELINUX_TOOK"));
 
     // Set libavb version for Framework-only OTA match in Treble build.
-    property_set("ro.boot.init.avb_version", std::to_string(AVB_MAJOR_VERSION).c_str());
+    const char* avb_version = getenv("INIT_AVB_VERSION");
+    if (avb_version) property_set("ro.boot.avb_version", avb_version);
 
     // Clean up our environment.
     unsetenv("INIT_SECOND_STAGE");
     unsetenv("INIT_STARTED_AT");
     unsetenv("INIT_SELINUX_TOOK");
+    unsetenv("INIT_AVB_VERSION");
 
     // Now set up SELinux for second stage.
     selinux_initialize(false);