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Commit d45c5091 authored by Kelvin Zhang's avatar Kelvin Zhang
Browse files

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
parent ad51f09b

fs_mgr/libsnapshot/libsnapshot_cow/test_v3.cpp

+17 −4
Original line number Diff line number Diff line
@@ -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 @@ TEST_F(CowTestV3, SetTypeSourceInverleave) { 
    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

+6 −1
Original line number Diff line number Diff line
@@ -327,7 +327,12 @@ bool CowWriterV3::EmitSequenceData(size_t num_ops, const uint32_t* data) { 
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;

    }