51 lines
1.8 KiB
Plaintext
51 lines
1.8 KiB
Plaintext
This is a device mapper block compression driver.
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Note:
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- Sectors are always 512 bytes (kernel constant).
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- Physical blocks are always 4kb (internal constant).
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- Logical blocks are variable 4kb .. 1gb.
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- All integers are little endian.
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Block device layout:
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- byte[4096] header
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/* Offset 0 */
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- byte[4] magic
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- u16 version_major
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- u16 version_minor
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- u16 flags
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- u8 algorithm (1=lz4, 2=zlib, ...) [1]
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- u8 compression (1..9) [1]
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- u16 pbat_len [1]
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- u16 lblk_shift (1..18) [4 = 64kb]
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- u64 nr_pblk
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- u32 nr_zones
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- u32 lblk_per_zone
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- byte[32] reserved
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/* Offset 64 */
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- u64 pblk_alloc
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- byte[] reserved
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- byte[] zone ... vector of zone
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Device size limits:
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- Min: header plus one zone (header, pbat, lbat, data)
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Arbitrarily limit to 1mb (?)
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- Max: 2^48 pblk = 1eb
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There are six different lblk_alloc sizes:
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Struct name Size lblk_size device_pblk_size
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=========== ==== ========= ================
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lblk_alloc_16_16 2+2*8 <= 64kb <= 64k
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lblk_alloc_16_32 2+4*8 <= 64kb <= 4g
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lblk_alloc_16_48 2+6*8 <= 64kb <= 256t
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lblk_alloc_32_16 4+2*8 > 64kb <= 64k
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lblk_alloc_32_32 4+4*8 > 64kb <= 4g
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lblk_alloc_32_48 4+6*8 > 64kb <= 256t
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Zone layout:
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- byte[4k*pbat_len] Physical block allocation table (pbat)
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- lblk_alloc_x_y[] Logical block allocation table (lbat)
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Note: padded to pblk size
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- data[4k*pbat_len*4k*8] Data
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One pblk per bit in pbat
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