libsnapshot: Zero out leftover ops in CowWriter
When opening in append mode, we could write less than what was present
before. This could result in data blocks referencing beyond the end of
the file, or partially written ops. Zeroing these out will prevent
invalid leftovers from potentially causing confusion.
Bug: 183985866
Test: cow_api_test
Change-Id: I56f0218f3ea5b83c0614d1b86e81a4ca885f5c5e
diff --git a/fs_mgr/libsnapshot/cow_api_test.cpp b/fs_mgr/libsnapshot/cow_api_test.cpp
index a4cf9b4..d06427e 100644
--- a/fs_mgr/libsnapshot/cow_api_test.cpp
+++ b/fs_mgr/libsnapshot/cow_api_test.cpp
@@ -869,6 +869,57 @@
ASSERT_EQ(num_clusters, 2);
}
+TEST_F(CowTest, DeleteMidCluster) {
+ CowOptions options;
+ options.cluster_ops = 7;
+ auto writer = std::make_unique<CowWriter>(options);
+ ASSERT_TRUE(writer->Initialize(cow_->fd));
+
+ ASSERT_TRUE(WriteDataBlock(writer.get(), 1, "Block 1"));
+ ASSERT_TRUE(WriteDataBlock(writer.get(), 2, "Block 2"));
+ ASSERT_TRUE(WriteDataBlock(writer.get(), 3, "Block 3"));
+ ASSERT_TRUE(writer->AddLabel(1));
+ ASSERT_TRUE(writer->Finalize());
+ ASSERT_TRUE(WriteDataBlock(writer.get(), 4, "Block 4"));
+ ASSERT_TRUE(WriteDataBlock(writer.get(), 5, "Block 5"));
+ ASSERT_TRUE(WriteDataBlock(writer.get(), 6, "Block 6"));
+ ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+ writer = std::make_unique<CowWriter>(options);
+ ASSERT_TRUE(writer->InitializeAppend(cow_->fd, 1));
+ ASSERT_TRUE(writer->Finalize());
+ ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+ CowReader reader;
+ ASSERT_TRUE(reader.Parse(cow_->fd));
+
+ auto iter = reader.GetOpIter();
+ size_t num_replace = 0;
+ size_t max_in_cluster = 0;
+ size_t num_in_cluster = 0;
+ size_t num_clusters = 0;
+ while (!iter->Done()) {
+ const auto& op = iter->Get();
+
+ num_in_cluster++;
+ max_in_cluster = std::max(max_in_cluster, num_in_cluster);
+ if (op.type == kCowReplaceOp) {
+ num_replace++;
+
+ ASSERT_EQ(op.new_block, num_replace);
+ ASSERT_TRUE(CompareDataBlock(&reader, op, "Block " + std::to_string(num_replace)));
+ } else if (op.type == kCowClusterOp) {
+ num_in_cluster = 0;
+ num_clusters++;
+ }
+
+ iter->Next();
+ }
+ ASSERT_EQ(num_replace, 3);
+ ASSERT_EQ(max_in_cluster, 5); // 3 data, 1 label, 1 cluster op
+ ASSERT_EQ(num_clusters, 1);
+}
+
} // namespace snapshot
} // namespace android
diff --git a/fs_mgr/libsnapshot/cow_writer.cpp b/fs_mgr/libsnapshot/cow_writer.cpp
index 5c7cc16..8fd1cc4 100644
--- a/fs_mgr/libsnapshot/cow_writer.cpp
+++ b/fs_mgr/libsnapshot/cow_writer.cpp
@@ -375,6 +375,21 @@
auto continue_num_ops = footer_.op.num_ops;
bool extra_cluster = false;
+ // Blank out extra ops, in case we're in append mode and dropped ops.
+ if (cluster_size_) {
+ auto unused_cluster_space = cluster_size_ - current_cluster_size_;
+ std::string clr;
+ clr.resize(unused_cluster_space, '\0');
+ if (lseek(fd_.get(), next_op_pos_, SEEK_SET) < 0) {
+ PLOG(ERROR) << "Failed to seek to footer position.";
+ return false;
+ }
+ if (!android::base::WriteFully(fd_, clr.data(), clr.size())) {
+ PLOG(ERROR) << "clearing unused cluster area failed";
+ return false;
+ }
+ }
+
// Footer should be at the end of a file, so if there is data after the current block, end it
// and start a new cluster.
if (cluster_size_ && current_data_size_ > 0) {