logd/SerializedLogChunk.h

/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

#include <sys/types.h>

#include <list>
#include <vector>

#include <android-base/logging.h>

#include "LogWriter.h"
#include "LogdLock.h"
#include "SerializedData.h"
#include "SerializedLogEntry.h"

class SerializedFlushToState;

class SerializedLogChunk {
  public:
    friend void VerifyChunks(const std::list<SerializedLogChunk>& expected,
                             const std::list<SerializedLogChunk>& chunks);

    class LogEntryIterator {
      public:
        LogEntryIterator(SerializedLogChunk& chunk, int read_offset_)
            : chunk_(chunk), read_offset_(read_offset_) {}

        LogEntryIterator& operator++() {
            read_offset_ += chunk_.log_entry(read_offset_)->total_len();
            return *this;
        }

        bool operator!=(const LogEntryIterator& other) const {
            return read_offset_ != other.read_offset_;
        }
        const SerializedLogEntry& operator*() const { return *chunk_.log_entry(read_offset_); }

      private:
        SerializedLogChunk& chunk_;
        int read_offset_;
    };

    explicit SerializedLogChunk(size_t size) : contents_(size) {}
    SerializedLogChunk(SerializedLogChunk&& other) noexcept = default;
    ~SerializedLogChunk();

    void FinishWriting();
    void IncReaderRefCount();
    void DecReaderRefCount();
    void AttachReader(SerializedFlushToState* reader);
    void DetachReader(SerializedFlushToState* reader);

    void NotifyReadersOfPrune(log_id_t log_id) REQUIRES(logd_lock);

    bool CanLog(size_t len);
    SerializedLogEntry* Log(uint64_t sequence, log_time realtime, uid_t uid, pid_t pid, pid_t tid,
                            const char* msg, uint16_t len);

    // If this buffer has been compressed, we only consider its compressed size when accounting for
    // memory consumption for pruning.  This is since the uncompressed log is only by used by
    // readers, and thus not a representation of how much these logs cost to keep in memory.
    size_t PruneSize() const {
        return sizeof(*this) + (compressed_log_.size() ?: contents_.size());
    }

    const SerializedLogEntry* log_entry(int offset) const {
        CHECK(writer_active_ || reader_ref_count_ > 0);
        return reinterpret_cast<const SerializedLogEntry*>(data() + offset);
    }
    const uint8_t* data() const { return contents_.data(); }
    int write_offset() const { return write_offset_; }
    uint64_t highest_sequence_number() const { return highest_sequence_number_; }

    LogEntryIterator begin() { return LogEntryIterator(*this, 0); }

    LogEntryIterator end() { return LogEntryIterator(*this, write_offset_); }

    // Exposed for testing
    uint32_t reader_ref_count() const { return reader_ref_count_; }

  private:
    // The decompressed contents of this log buffer.  Deallocated when the ref_count reaches 0 and
    // writer_active_ is false.
    SerializedData contents_;
    int write_offset_ = 0;
    uint32_t reader_ref_count_ = 0;
    bool writer_active_ = true;
    uint64_t highest_sequence_number_ = 1;
    SerializedData compressed_log_;
    std::vector<SerializedFlushToState*> readers_;
};