libsnapshot: no overlayfs during virtual a/b ota.

With overlayfs enabled, the scratch partition takes up
super partition, causing retrofit devices to create COW
images.
Test: OTA on retrofit device, no COW images created.

Change-Id: I35a1a2d02c8acf9efc33965c7e015f960bf45296

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

@@ -100,6 +100,7 @@ class SnapshotManager final {
         virtual std::string GetSlotSuffix() const = 0;
         virtual std::string GetSuperDevice(uint32_t slot) const = 0;
         virtual const IPartitionOpener& GetPartitionOpener() const = 0;
+        virtual bool IsOverlayfsSetup() const = 0;
     };
 
     ~SnapshotManager();

fs_mgr/libsnapshot/snapshot.cpp

@@ -32,6 +32,7 @@
 #include <ext4_utils/ext4_utils.h>
 #include <fs_mgr.h>
 #include <fs_mgr_dm_linear.h>
+#include <fs_mgr_overlayfs.h>
 #include <fstab/fstab.h>
 #include <libdm/dm.h>
 #include <libfiemap/image_manager.h>
@@ -77,6 +78,7 @@ class DeviceInfo final : public SnapshotManager::IDeviceInfo {
     std::string GetSuperDevice(uint32_t slot) const override {
         return fs_mgr_get_super_partition_name(slot);
     }
+    bool IsOverlayfsSetup() const override { return fs_mgr_overlayfs_is_setup(); }
 
   private:
     android::fs_mgr::PartitionOpener opener_;
@@ -1731,6 +1733,15 @@ bool SnapshotManager::CreateUpdateSnapshots(MetadataBuilder* target_metadata,
         return false;
     }
 
+    // TODO(b/134949511): remove this check. Right now, with overlayfs mounted, the scratch
+    // partition takes up a big chunk of space in super, causing COW images to be created on
+    // retrofit Virtual A/B devices.
+    if (device_->IsOverlayfsSetup()) {
+        LOG(ERROR) << "Cannot create update snapshots with overlayfs setup. Run `adb enable-verity`"
+                   << ", reboot, then try again.";
+        return false;
+    }
+
     // Check that all these metadata is not retrofit dynamic partitions. Snapshots on
     // devices with retrofit dynamic partitions does not make sense.
     // This ensures that current_metadata->GetFreeRegions() uses the same device

fs_mgr/libsnapshot/test_helpers.h

@@ -51,6 +51,7 @@ class TestDeviceInfo : public SnapshotManager::IDeviceInfo {
     const android::fs_mgr::IPartitionOpener& GetPartitionOpener() const override {
         return *opener_.get();
     }
+    bool IsOverlayfsSetup() const override { return false; }
 
     void set_slot_suffix(const std::string& suffix) { slot_suffix_ = suffix; }
     void set_fake_super(const std::string& path) {