libsnapshot: Add a compression bit to SnapshotUpdateStatus.

This adds a compression bit to SnapshotUpdateStatus. This is so init can
tell whether it needs to launch snapuserd, without reading the
individual state of each snapshot, since this state is global.

Bug: 173476209
Test: manual test
Change-Id: I8c3bbfb0d184f70e661e7b043afc37e335d1e187

fs_mgr/libsnapshot/android/snapshot/snapshot.proto

@@ -118,7 +118,7 @@ enum UpdateState {
     Cancelled = 7;
 };
 
-// Next: 5
+// Next: 6
 message SnapshotUpdateStatus {
     UpdateState state = 1;
 
@@ -133,6 +133,9 @@ message SnapshotUpdateStatus {
 
     // Sectors allocated for metadata in all the snapshot devices.
     uint64 metadata_sectors = 4;
+
+    // Whether compression/dm-user was used for any snapshots.
+    bool compression_enabled = 5;
 }
 
 // Next: 4

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

@@ -353,6 +353,10 @@ class SnapshotManager final : public ISnapshotManager {
         uevent_regen_callback_ = callback;
     }
 
+    // If true, compression is enabled for this update. This is used by
+    // first-stage to decide whether to launch snapuserd.
+    bool IsSnapuserdRequired();
+
   private:
     FRIEND_TEST(SnapshotTest, CleanFirstStageMount);
     FRIEND_TEST(SnapshotTest, CreateSnapshot);

fs_mgr/libsnapshot/snapshot.cpp

@@ -2283,6 +2283,7 @@ SnapshotUpdateStatus SnapshotManager::ReadSnapshotUpdateStatus(LockedFile* lock)
 bool SnapshotManager::WriteUpdateState(LockedFile* lock, UpdateState state) {
     SnapshotUpdateStatus status = {};
     status.set_state(state);
+    status.set_compression_enabled(IsCompressionEnabled());
     return WriteSnapshotUpdateStatus(lock, status);
 }
 
@@ -2855,7 +2856,7 @@ std::unique_ptr<ISnapshotWriter> SnapshotManager::OpenSnapshotWriter(
         return nullptr;
     }
 
-    if (IsCompressionEnabled()) {
+    if (status.compression_enabled()) {
         return OpenCompressedSnapshotWriter(lock.get(), source_device, params.GetPartitionName(),
                                             status, paths);
     }
@@ -3346,5 +3347,13 @@ bool SnapshotManager::WaitForDevice(const std::string& device,
     return true;
 }
 
+bool SnapshotManager::IsSnapuserdRequired() {
+    auto lock = LockExclusive();
+    if (!lock) return false;
+
+    auto status = ReadSnapshotUpdateStatus(lock.get());
+    return status.state() != UpdateState::None && status.compression_enabled();
+}
+
 }  // namespace snapshot
 }  // namespace android