libsnapshot: Add a skeleton API for mapping and unmapping all snapshots.

Bug: 168554689
Test: builds
Change-Id: I0da50275cc4d0a85bd6b176b5c1286659d51a25c

fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot.h

@@ -47,6 +47,8 @@ class MockSnapshotManager : public ISnapshotManager {
     MOCK_METHOD(bool, CreateLogicalAndSnapshotPartitions,
                 (const std::string& super_device, const std::chrono::milliseconds& timeout_ms),
                 (override));
+    MOCK_METHOD(bool, MapAllSnapshots, (const std::chrono::milliseconds& timeout_ms), (override));
+    MOCK_METHOD(bool, UnmapAllSnapshots, (), (override));
     MOCK_METHOD(bool, HandleImminentDataWipe, (const std::function<void()>& callback), (override));
     MOCK_METHOD(bool, FinishMergeInRecovery, (), (override));
     MOCK_METHOD(CreateResult, RecoveryCreateSnapshotDevices, (), (override));

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

@@ -206,6 +206,14 @@ class ISnapshotManager {
     virtual bool CreateLogicalAndSnapshotPartitions(
             const std::string& super_device, const std::chrono::milliseconds& timeout_ms = {}) = 0;
 
+    // Map all snapshots. This is analogous to CreateLogicalAndSnapshotPartitions, except it maps
+    // the target slot rather than the current slot. It should only be used immediately after
+    // applying an update, before rebooting to the new slot.
+    virtual bool MapAllSnapshots(const std::chrono::milliseconds& timeout_ms = {}) = 0;
+
+    // Unmap all snapshots. This should be called to undo MapAllSnapshots().
+    virtual bool UnmapAllSnapshots() = 0;
+
     // This method should be called preceding any wipe or flash of metadata or
     // userdata. It is only valid in recovery or fastbootd, and it ensures that
     // a merge has been completed.
@@ -321,6 +329,8 @@ class SnapshotManager final : public ISnapshotManager {
     bool Dump(std::ostream& os) override;
     std::unique_ptr<AutoDevice> EnsureMetadataMounted() override;
     ISnapshotMergeStats* GetSnapshotMergeStatsInstance() override;
+    bool MapAllSnapshots(const std::chrono::milliseconds& timeout_ms = {}) override;
+    bool UnmapAllSnapshots() override;
 
   private:
     FRIEND_TEST(SnapshotTest, CleanFirstStageMount);

fs_mgr/libsnapshot/include/libsnapshot/snapshot_stub.h

@@ -52,6 +52,8 @@ class SnapshotManagerStub : public ISnapshotManager {
     bool Dump(std::ostream& os) override;
     std::unique_ptr<AutoDevice> EnsureMetadataMounted() override;
     ISnapshotMergeStats* GetSnapshotMergeStatsInstance() override;
+    bool MapAllSnapshots(const std::chrono::milliseconds& timeout_ms) override;
+    bool UnmapAllSnapshots() override;
 };
 
 }  // namespace android::snapshot

fs_mgr/libsnapshot/snapshot.cpp

@@ -1861,6 +1861,16 @@ bool SnapshotManager::UnmapCowDevices(LockedFile* lock, const std::string& name)
     return true;
 }
 
+bool SnapshotManager::MapAllSnapshots(const std::chrono::milliseconds&) {
+    LOG(ERROR) << "Not yet implemented.";
+    return false;
+}
+
+bool SnapshotManager::UnmapAllSnapshots() {
+    LOG(ERROR) << "Not yet implemented.";
+    return false;
+}
+
 auto SnapshotManager::OpenFile(const std::string& file, int lock_flags)
         -> std::unique_ptr<LockedFile> {
     unique_fd fd(open(file.c_str(), O_RDONLY | O_CLOEXEC | O_NOFOLLOW));

fs_mgr/libsnapshot/snapshot_stub.cpp

@@ -136,4 +136,14 @@ std::unique_ptr<ISnapshotWriter> SnapshotManagerStub::OpenSnapshotWriter(
     return nullptr;
 }
 
+bool SnapshotManagerStub::MapAllSnapshots(const std::chrono::milliseconds&) {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
+bool SnapshotManagerStub::UnmapAllSnapshots() {
+    LOG(ERROR) << __FUNCTION__ << " should never be called.";
+    return false;
+}
+
 }  // namespace android::snapshot