Re: Adding compression support for bluestore.

[Sage Weil <sage@newdream.net>]

How about this:

// in the onode:
map<uint64_t, bluestore_lextent_t> data_map;
map<int, bluestore_blob_t> blob_map;

// in the enode
map<int, bluestore_blob_t> blob_map;

struct bluestore_lextent_t {
  enum {
    FLAG_SHARED = 1,        ///< pextent lives in enode
  };

  uint64_t logical_length;  ///< length of logical bytes we represent
  uint32_t pextent_id;      ///< id of pextent in onode or enode
  uint32_t x_off, x_len;    ///< relative portion of pextent with our data
  uint32_t flags;           ///< FLAG_*
};

struct bluestore_pextent_t {
  uint64_t offset;          ///< offset on disk
  uint64_t length;          ///< length on disk
};

struct bluestore_blob_t {
  enum {
    CSUM_XXHASH32 = 1,
    CSUM_XXHASH64 = 2,
    CSUM_CRC32C = 3,
    CSUM_CRC16 = 4,
  };
  enum {
    FLAG_IMMUTABLE = 1,     ///< no overwrites allowed
    FLAG_COMPRESSED = 2,    ///< extent is compressed; alg is in first byte of data
  };
  enum {
    COMP_ZLIB = 1,
    COMP_SNAPPY = 2,
    COMP_LZO = 3,
  };

  vector<bluestore_pextent_t> extents;  ///< extents on disk
  uint32_t logical_length;              ///< uncompressed length
  uint32_t flags;                       ///< FLAG_*
  uint8_t csum_type;                    ///< CSUM_*
  uint8_t csum_block_order;
  uint16_t num_refs;               ///< reference count (always 1 when in onode)
  vector<char> csum_data;          ///< opaque vector of csum data

  uint32_t get_ondisk_length() const {
    uint32_t len = 0;
    for (auto &p : extentes) {
      len += p.length;
    }
    return len;
  }

  uint32_t get_csum_block_size() const {
    return 1 << csum_block_order;
  }
  size_t get_csum_value_size() const {
    switch (csum_type) {
    case CSUM_XXHASH32: return 4;
    case CSUM_XXHASH64: return 8;
    case CSUM_CRC32C: return 4;
    case CSUM_CRC16: return 2;
    default: return 0;
    }
  }

  // assert (ondisk_length / csum_block_size) * csum_value_size ==
  // csum_data.length()
};