ceph/src/rocksdb/db/blob/blob_log_sequential_reader.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5 //
   6 #pragma once
   7
   8 #include <memory>
   9
  10 #include "db/blob/blob_log_format.h"
  11 #include "rocksdb/slice.h"
  12
  13 #define MAX_HEADER_SIZE(a, b, c) (a > b ? (a > c ? a : c) : (b > c ? b : c))
  14
  15 namespace ROCKSDB_NAMESPACE {
  16
  17 class RandomAccessFileReader;
  18 class Env;
  19 class Statistics;
  20 class Status;
  21 class SystemClock;
  22
  23 /**
  24  * BlobLogSequentialReader is a general purpose log stream reader
  25  * implementation. The actual job of reading from the device is implemented by
  26  * the RandomAccessFileReader interface.
  27  *
  28  * Please see BlobLogWriter for details on the file and record layout.
  29  */
  30
  31 class BlobLogSequentialReader {
  32  public:
  33   enum ReadLevel {
  34     kReadHeader,
  35     kReadHeaderKey,
  36     kReadHeaderKeyBlob,
  37   };
  38
  39   // Create a reader that will return log records from "*file_reader".
  40   BlobLogSequentialReader(std::unique_ptr<RandomAccessFileReader>&& file_reader,
  41                           SystemClock* clock, Statistics* statistics);
  42
  43   // No copying allowed
  44   BlobLogSequentialReader(const BlobLogSequentialReader&) = delete;
  45   BlobLogSequentialReader& operator=(const BlobLogSequentialReader&) = delete;
  46
  47   ~BlobLogSequentialReader();
  48
  49   Status ReadHeader(BlobLogHeader* header);
  50
  51   // Read the next record into *record.  Returns true if read
  52   // successfully, false if we hit end of the input. The contents filled in
  53   // *record will only be valid until the next mutating operation on this
  54   // reader.
  55   // If blob_offset is non-null, return offset of the blob through it.
  56   Status ReadRecord(BlobLogRecord* record, ReadLevel level = kReadHeader,
  57                     uint64_t* blob_offset = nullptr);
  58
  59   Status ReadFooter(BlobLogFooter* footer);
  60
  61   void ResetNextByte() { next_byte_ = 0; }
  62
  63   uint64_t GetNextByte() const { return next_byte_; }
  64
  65  private:
  66   Status ReadSlice(uint64_t size, Slice* slice, char* buf);
  67
  68   const std::unique_ptr<RandomAccessFileReader> file_;
  69   SystemClock* clock_;
  70
  71   Statistics* statistics_;
  72
  73   Slice buffer_;
  74   char header_buf_[MAX_HEADER_SIZE(BlobLogHeader::kSize, BlobLogFooter::kSize,
  75                                    BlobLogRecord::kHeaderSize)];
  76
  77   // which byte to read next
  78   uint64_t next_byte_;
  79 };
  80
  81 }  // namespace ROCKSDB_NAMESPACE
  82
  83 #undef MAX_HEADER_SIZE