ceph bluestore Blob 分析

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ceph version: 11.0.0

bluestore 包含一个非常重要的结构， Blob, 本节主要分析 Blob， 注意 ceph 版本是基于 11.0.0 的。

1. Blob

struct Blob : public boost::intrusive::set_base_hook<> {
  int64_t id = 0;          ///< id
  bluestore_blob_t blob;   ///< blob metadata
  BufferSpace bc;          ///< buffer cache
...

}

Blob 包含三个数据:

id: id

blob: blob metadata

bc: 逻辑 extent 到 buffeffer 映射

之后是 Blob 的构造函数和析构函数等。

2. bluestore_blob_t

struct bluestore_blob_t {
...
  vector<bluestore_pextent_t> extents;///< raw data position on device
  uint32_t compressed_length = 0;     ///< compressed length if any
  uint32_t flags = 0;                 ///< FLAG_*

  uint8_t csum_type = CSUM_NONE;      ///< CSUM_*
  uint8_t csum_chunk_order = 0;       ///< csum block size is 1<<block_order bytes

  bluestore_extent_ref_map_t ref_map; ///< references (empty when in onode)
  bufferptr csum_data;                ///< opaque vector of csum data

  typedef uint16_t unused_uint_t;
  typedef std::bitset<sizeof(unused_uint_t) * 8> unused_t;
  unused_t unused;                    ///< portion that has never been written to
...
}

extents: 对应物理设备上的原始数据

compresed_length: 数据压缩后的长度

flags:

    FLAG_MUTABLE = 1,         ///< blob can be overwritten or split
    FLAG_COMPRESSED = 2,      ///< blob is compressed
    FLAG_CSUM = 4,            ///< blob has checksums
    FLAG_HAS_UNUSED = 8,      ///< blob has unused map

csum_type:

    CSUM_NONE = 0,
    CSUM_XXHASH32 = 1,
    CSUM_XXHASH64 = 2,
    CSUM_CRC32C = 3,
    CSUM_CRC32C_16 = 4, // low 16 bits of crc32c
    CSUM_CRC32C_8 = 5,  // low 8 bits of crc32c
    CSUM_MAX,

csum_chunk_order: csum 块大小， 1 << csum_chunk_order

ref_map: references

csum_data: check sum data

3. BufferSpace

struct BufferSpace {
...
  map<uint64_t,std::unique_ptr<Buffer>> buffer_map;
  Cache *cache;
  state_list_t writing;
...
}