libsnapshot: Check if the vendor is updated from Android S for GRF

In a GRF config, if Vendor partition is updated from Android 12; post
OTA reboot, first stage init will communicate to daemon to check if the
daemon can support socket handoff. If that succeeds, then it is a signal
that the vendor has been updated from Android 12. Use a marker in
/metadata to signal that the vendor was updated. If the marker is present,
then post OTA reboot, userspace snapshot will be used.

Bug: 333854394
Test: OTA
Android U (system) + S (vendor) -> Android V (system) + V (Vendor)

Change-Id: Ie38c4379010789a84e5b44529b407f9f82135271
Signed-off-by: Akilesh Kailash <akailash@google.com>

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

@@ -335,6 +335,9 @@ class SnapshotManager final : public ISnapshotManager {
     // after loading selinux policy.
     bool PrepareSnapuserdArgsForSelinux(std::vector<std::string>* snapuserd_argv);
 
+    // If snapuserd from first stage init was started from system partition.
+    bool MarkSnapuserdFromSystem();
+
     // Detach dm-user devices from the first stage snapuserd. Load
     // new dm-user tables after loading selinux policy.
     bool DetachFirstStageSnapuserdForSelinux();
@@ -670,6 +673,7 @@ class SnapshotManager final : public ISnapshotManager {
     std::string GetForwardMergeIndicatorPath();
     std::string GetOldPartitionMetadataPath();
     std::string GetBootSnapshotsWithoutSlotSwitchPath();
+    std::string GetSnapuserdFromSystemPath();
 
     const LpMetadata* ReadOldPartitionMetadata(LockedFile* lock);
 

fs_mgr/libsnapshot/snapshot.cpp

@@ -88,6 +88,7 @@ static constexpr char kBootSnapshotsWithoutSlotSwitch[] =
         "/metadata/ota/snapshot-boot-without-slot-switch";
 static constexpr char kBootIndicatorPath[] = "/metadata/ota/snapshot-boot";
 static constexpr char kRollbackIndicatorPath[] = "/metadata/ota/rollback-indicator";
+static constexpr char kSnapuserdFromSystem[] = "/metadata/ota/snapuserd-from-system";
 static constexpr auto kUpdateStateCheckInterval = 2s;
 /*
  * The readahead size is set to 32kb so that
@@ -318,7 +319,7 @@ bool SnapshotManager::RemoveAllUpdateState(LockedFile* lock, const std::function
     std::vector<std::string> files = {
             GetSnapshotBootIndicatorPath(),          GetRollbackIndicatorPath(),
             GetForwardMergeIndicatorPath(),          GetOldPartitionMetadataPath(),
-            GetBootSnapshotsWithoutSlotSwitchPath(),
+            GetBootSnapshotsWithoutSlotSwitchPath(), GetSnapuserdFromSystemPath(),
     };
     for (const auto& file : files) {
         RemoveFileIfExists(file);
@@ -1457,6 +1458,10 @@ std::string SnapshotManager::GetRollbackIndicatorPath() {
     return metadata_dir_ + "/" + android::base::Basename(kRollbackIndicatorPath);
 }
 
+std::string SnapshotManager::GetSnapuserdFromSystemPath() {
+    return metadata_dir_ + "/" + android::base::Basename(kSnapuserdFromSystem);
+}
+
 std::string SnapshotManager::GetForwardMergeIndicatorPath() {
     return metadata_dir_ + "/allow-forward-merge";
 }
@@ -2122,6 +2127,16 @@ bool SnapshotManager::UpdateUsesODirect(LockedFile* lock) {
     return update_status.o_direct();
 }
 
+bool SnapshotManager::MarkSnapuserdFromSystem() {
+    auto path = GetSnapuserdFromSystemPath();
+
+    if (!android::base::WriteStringToFile("1", path)) {
+        PLOG(ERROR) << "Unable to write to vendor update path: " << path;
+        return false;
+    }
+    return true;
+}
+
 /*
  * Please see b/304829384 for more details.
  *
@@ -2158,11 +2173,26 @@ bool SnapshotManager::UpdateUsesODirect(LockedFile* lock) {
  *         iii: If both (i) and (ii) are true, then use the dm-snapshot based
  *         approach.
  *
+ * 3: Post OTA reboot, if the vendor partition was updated from Android 12 to
+ * any other release post Android 12, then snapuserd binary will be "system"
+ * partition as post Android 12, init_boot will contain a copy of snapuserd
+ * binary. Thus, during first stage init, if init is able to communicate to
+ * daemon, that gives us a signal that the binary is from "system" copy. Hence,
+ * there is no need to fallback to legacy dm-snapshot. Thus, init will use a
+ * marker in /metadata to signal that the snapuserd binary from first stage init
+ * can handle userspace snapshots.
+ *
  */
 bool SnapshotManager::IsLegacySnapuserdPostReboot() {
     if (is_legacy_snapuserd_.has_value() && is_legacy_snapuserd_.value() == true) {
         auto slot = GetCurrentSlot();
         if (slot == Slot::Target) {
+            // If this marker is present, then daemon can handle userspace
+            // snapshots; also, it indicates that the vendor partition was
+            // updated from Android 12.
+            if (access(GetSnapuserdFromSystemPath().c_str(), F_OK) == 0) {
+                return false;
+            }
             return true;
         }
     }

init/first_stage_mount.cpp

@@ -395,12 +395,7 @@ bool FirstStageMountVBootV2::CreateSnapshotPartitions(SnapshotManager* sm) {
 
     use_snapuserd_ = sm->IsSnapuserdRequired();
     if (use_snapuserd_) {
-        if (sm->UpdateUsesUserSnapshots()) {
-            LaunchFirstStageSnapuserd();
-        } else {
-            LOG(FATAL) << "legacy virtual-ab is no longer supported";
-            return false;
-        }
+        LaunchFirstStageSnapuserd();
     }
 
     sm->SetUeventRegenCallback([this](const std::string& device) -> bool {

init/snapuserd_transition.cpp

@@ -100,6 +100,10 @@ void LaunchFirstStageSnapuserd() {
     }
     if (client->SupportsSecondStageSocketHandoff()) {
         setenv(kSnapuserdFirstStageInfoVar, "socket", 1);
+        auto sm = SnapshotManager::NewForFirstStageMount();
+        if (!sm->MarkSnapuserdFromSystem()) {
+            LOG(ERROR) << "Failed to update MarkSnapuserdFromSystem";
+        }
     }
 
     setenv(kSnapuserdFirstStagePidVar, std::to_string(pid).c_str(), 1);