Re: Adding compression support for bluestore.

[Igor Fedotov <ifedotov@mirantis.com>]

On 01.04.2016 0:56, Sage Weil wrote:
> 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
And I'd prefer 64-bit integer for this field as 4 Gb overwrites can 
overflow the corresponding counter. That's just 4Tb data written by 4K 
blocks.

>    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()
> };