commit d45c50911f989caacc6c46f79ee2e4fd66615c65
author Kelvin Zhang <zhangkelvin@google.com> Tue Dec 05 15:21:46 2023 -0800
committer Kelvin Zhang <zhangkelvin@google.com> Tue Dec 05 21:27:38 2023 -0800
tree 43a469e1de0b8f31dd749f452f3a33f83754c600
parent ad51f09b050d87ae284261d7566ee929defd757d

Fix cow v3 size estimation errors

Current cow size estimation is computed by taking the offset of next
data write. However, during COW size estimation we repeatdly increment
op_count_max. Since data section is placed right after op section,
incrementing  op_count_max has the effect of moving the beginning of
data section. next_data_pos_ is never updated in this process, causing
the final estiamte to be off.

Test: th
Bug: 313962438
Change-Id: I250dff54c470c9c20d6db33d91bac898358dee31

fs_mgr/libsnapshot/libsnapshot_cow/test_v3.cpp

diff --git a/fs_mgr/libsnapshot/libsnapshot_cow/test_v3.cpp b/fs_mgr/libsnapshot/libsnapshot_cow/test_v3.cpp
index aceed24..27accdc 100644
--- a/fs_mgr/libsnapshot/libsnapshot_cow/test_v3.cpp
+++ b/fs_mgr/libsnapshot/libsnapshot_cow/test_v3.cpp
@@ -15,17 +15,15 @@
 #include <sys/stat.h>
 
 #include <cstdio>
-#include <iostream>
 #include <memory>
-#include <string_view>
 
 #include <android-base/file.h>
 #include <android-base/logging.h>
+#include <android-base/unique_fd.h>
 #include <gtest/gtest.h>
+#include <libsnapshot/cow_format.h>
 #include <libsnapshot/cow_reader.h>
 #include <libsnapshot/cow_writer.h>
-#include "cow_decompress.h"
-#include "libsnapshot/cow_format.h"
 #include "writer_v2.h"
 #include "writer_v3.h"
 
@@ -658,5 +656,20 @@
     ASSERT_EQ(op.type(), kCowReplaceOp);
 }
 
+TEST_F(CowTestV3, CowSizeEstimate) {
+    CowOptions options{};
+    options.compression = "none";
+    auto estimator = android::snapshot::CreateCowEstimator(3, options);
+    ASSERT_TRUE(estimator->AddZeroBlocks(0, 1024 * 1024));
+    const auto cow_size = estimator->GetCowSize();
+    options.op_count_max = 1024 * 1024;
+    options.max_blocks = 1024 * 1024;
+    CowWriterV3 writer(options, GetCowFd());
+    ASSERT_TRUE(writer.Initialize());
+    ASSERT_TRUE(writer.AddZeroBlocks(0, 1024 * 1024));
+
+    ASSERT_LE(writer.GetCowSize(), cow_size);
+}
+
 }  // namespace snapshot
 }  // namespace android

fs_mgr/libsnapshot/libsnapshot_cow/writer_v3.cpp

diff --git a/fs_mgr/libsnapshot/libsnapshot_cow/writer_v3.cpp b/fs_mgr/libsnapshot/libsnapshot_cow/writer_v3.cpp
index 5bdc5fd..07f6f00 100644
--- a/fs_mgr/libsnapshot/libsnapshot_cow/writer_v3.cpp
+++ b/fs_mgr/libsnapshot/libsnapshot_cow/writer_v3.cpp
@@ -327,7 +327,12 @@
 bool CowWriterV3::WriteOperation(const CowOperationV3& op, const void* data, size_t size) {
     if (IsEstimating()) {
         header_.op_count++;
-        header_.op_count_max++;
+        if (header_.op_count > header_.op_count_max) {
+            // If we increment op_count_max, the offset of data section would
+            // change. So need to update |next_data_pos_|
+            next_data_pos_ += (header_.op_count - header_.op_count_max) * sizeof(CowOperationV3);
+            header_.op_count_max = header_.op_count;
+        }
         next_data_pos_ += op.data_length;
         return true;
     }