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295 lines
8.2 KiB
C
295 lines
8.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _BCACHEFS_EXTENTS_FORMAT_H
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#define _BCACHEFS_EXTENTS_FORMAT_H
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/*
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* In extent bkeys, the value is a list of pointers (bch_extent_ptr), optionally
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* preceded by checksum/compression information (bch_extent_crc32 or
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* bch_extent_crc64).
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*
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* One major determining factor in the format of extents is how we handle and
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* represent extents that have been partially overwritten and thus trimmed:
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*
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* If an extent is not checksummed or compressed, when the extent is trimmed we
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* don't have to remember the extent we originally allocated and wrote: we can
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* merely adjust ptr->offset to point to the start of the data that is currently
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* live. The size field in struct bkey records the current (live) size of the
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* extent, and is also used to mean "size of region on disk that we point to" in
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* this case.
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*
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* Thus an extent that is not checksummed or compressed will consist only of a
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* list of bch_extent_ptrs, with none of the fields in
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* bch_extent_crc32/bch_extent_crc64.
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*
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* When an extent is checksummed or compressed, it's not possible to read only
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* the data that is currently live: we have to read the entire extent that was
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* originally written, and then return only the part of the extent that is
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* currently live.
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*
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* Thus, in addition to the current size of the extent in struct bkey, we need
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* to store the size of the originally allocated space - this is the
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* compressed_size and uncompressed_size fields in bch_extent_crc32/64. Also,
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* when the extent is trimmed, instead of modifying the offset field of the
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* pointer, we keep a second smaller offset field - "offset into the original
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* extent of the currently live region".
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*
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* The other major determining factor is replication and data migration:
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*
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* Each pointer may have its own bch_extent_crc32/64. When doing a replicated
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* write, we will initially write all the replicas in the same format, with the
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* same checksum type and compression format - however, when copygc runs later (or
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* tiering/cache promotion, anything that moves data), it is not in general
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* going to rewrite all the pointers at once - one of the replicas may be in a
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* bucket on one device that has very little fragmentation while another lives
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* in a bucket that has become heavily fragmented, and thus is being rewritten
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* sooner than the rest.
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*
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* Thus it will only move a subset of the pointers (or in the case of
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* tiering/cache promotion perhaps add a single pointer without dropping any
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* current pointers), and if the extent has been partially overwritten it must
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* write only the currently live portion (or copygc would not be able to reduce
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* fragmentation!) - which necessitates a different bch_extent_crc format for
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* the new pointer.
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*
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* But in the interests of space efficiency, we don't want to store one
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* bch_extent_crc for each pointer if we don't have to.
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*
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* Thus, a bch_extent consists of bch_extent_crc32s, bch_extent_crc64s, and
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* bch_extent_ptrs appended arbitrarily one after the other. We determine the
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* type of a given entry with a scheme similar to utf8 (except we're encoding a
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* type, not a size), encoding the type in the position of the first set bit:
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*
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* bch_extent_crc32 - 0b1
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* bch_extent_ptr - 0b10
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* bch_extent_crc64 - 0b100
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*
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* We do it this way because bch_extent_crc32 is _very_ constrained on bits (and
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* bch_extent_crc64 is the least constrained).
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*
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* Then, each bch_extent_crc32/64 applies to the pointers that follow after it,
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* until the next bch_extent_crc32/64.
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*
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* If there are no bch_extent_crcs preceding a bch_extent_ptr, then that pointer
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* is neither checksummed nor compressed.
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*/
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#define BCH_EXTENT_ENTRY_TYPES() \
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x(ptr, 0) \
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x(crc32, 1) \
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x(crc64, 2) \
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x(crc128, 3) \
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x(stripe_ptr, 4) \
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x(rebalance, 5)
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#define BCH_EXTENT_ENTRY_MAX 6
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enum bch_extent_entry_type {
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#define x(f, n) BCH_EXTENT_ENTRY_##f = n,
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BCH_EXTENT_ENTRY_TYPES()
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#undef x
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};
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/* Compressed/uncompressed size are stored biased by 1: */
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struct bch_extent_crc32 {
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#if defined(__LITTLE_ENDIAN_BITFIELD)
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__u32 type:2,
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_compressed_size:7,
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_uncompressed_size:7,
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offset:7,
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_unused:1,
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csum_type:4,
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compression_type:4;
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__u32 csum;
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#elif defined (__BIG_ENDIAN_BITFIELD)
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__u32 csum;
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__u32 compression_type:4,
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csum_type:4,
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_unused:1,
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offset:7,
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_uncompressed_size:7,
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_compressed_size:7,
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type:2;
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#endif
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} __packed __aligned(8);
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#define CRC32_SIZE_MAX (1U << 7)
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#define CRC32_NONCE_MAX 0
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struct bch_extent_crc64 {
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#if defined(__LITTLE_ENDIAN_BITFIELD)
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__u64 type:3,
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_compressed_size:9,
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_uncompressed_size:9,
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offset:9,
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nonce:10,
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csum_type:4,
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compression_type:4,
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csum_hi:16;
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#elif defined (__BIG_ENDIAN_BITFIELD)
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__u64 csum_hi:16,
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compression_type:4,
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csum_type:4,
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nonce:10,
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offset:9,
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_uncompressed_size:9,
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_compressed_size:9,
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type:3;
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#endif
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__u64 csum_lo;
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} __packed __aligned(8);
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#define CRC64_SIZE_MAX (1U << 9)
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#define CRC64_NONCE_MAX ((1U << 10) - 1)
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struct bch_extent_crc128 {
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#if defined(__LITTLE_ENDIAN_BITFIELD)
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__u64 type:4,
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_compressed_size:13,
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_uncompressed_size:13,
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offset:13,
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nonce:13,
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csum_type:4,
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compression_type:4;
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#elif defined (__BIG_ENDIAN_BITFIELD)
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__u64 compression_type:4,
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csum_type:4,
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nonce:13,
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offset:13,
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_uncompressed_size:13,
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_compressed_size:13,
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type:4;
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#endif
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struct bch_csum csum;
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} __packed __aligned(8);
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#define CRC128_SIZE_MAX (1U << 13)
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#define CRC128_NONCE_MAX ((1U << 13) - 1)
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/*
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* @reservation - pointer hasn't been written to, just reserved
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*/
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struct bch_extent_ptr {
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#if defined(__LITTLE_ENDIAN_BITFIELD)
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__u64 type:1,
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cached:1,
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unused:1,
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unwritten:1,
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offset:44, /* 8 petabytes */
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dev:8,
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gen:8;
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#elif defined (__BIG_ENDIAN_BITFIELD)
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__u64 gen:8,
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dev:8,
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offset:44,
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unwritten:1,
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unused:1,
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cached:1,
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type:1;
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#endif
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} __packed __aligned(8);
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struct bch_extent_stripe_ptr {
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#if defined(__LITTLE_ENDIAN_BITFIELD)
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__u64 type:5,
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block:8,
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redundancy:4,
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idx:47;
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#elif defined (__BIG_ENDIAN_BITFIELD)
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__u64 idx:47,
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redundancy:4,
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block:8,
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type:5;
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#endif
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};
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struct bch_extent_rebalance {
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#if defined(__LITTLE_ENDIAN_BITFIELD)
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__u64 type:6,
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unused:34,
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compression:8, /* enum bch_compression_opt */
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target:16;
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#elif defined (__BIG_ENDIAN_BITFIELD)
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__u64 target:16,
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compression:8,
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unused:34,
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type:6;
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#endif
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};
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union bch_extent_entry {
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#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ || __BITS_PER_LONG == 64
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unsigned long type;
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#elif __BITS_PER_LONG == 32
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struct {
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unsigned long pad;
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unsigned long type;
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};
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#else
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#error edit for your odd byteorder.
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#endif
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#define x(f, n) struct bch_extent_##f f;
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BCH_EXTENT_ENTRY_TYPES()
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#undef x
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};
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struct bch_btree_ptr {
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struct bch_val v;
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__u64 _data[0];
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struct bch_extent_ptr start[];
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} __packed __aligned(8);
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struct bch_btree_ptr_v2 {
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struct bch_val v;
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__u64 mem_ptr;
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__le64 seq;
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__le16 sectors_written;
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__le16 flags;
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struct bpos min_key;
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__u64 _data[0];
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struct bch_extent_ptr start[];
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} __packed __aligned(8);
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LE16_BITMASK(BTREE_PTR_RANGE_UPDATED, struct bch_btree_ptr_v2, flags, 0, 1);
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struct bch_extent {
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struct bch_val v;
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__u64 _data[0];
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union bch_extent_entry start[];
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} __packed __aligned(8);
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/* Maximum size (in u64s) a single pointer could be: */
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#define BKEY_EXTENT_PTR_U64s_MAX\
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((sizeof(struct bch_extent_crc128) + \
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sizeof(struct bch_extent_ptr)) / sizeof(__u64))
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/* Maximum possible size of an entire extent value: */
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#define BKEY_EXTENT_VAL_U64s_MAX \
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(1 + BKEY_EXTENT_PTR_U64s_MAX * (BCH_REPLICAS_MAX + 1))
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/* * Maximum possible size of an entire extent, key + value: */
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#define BKEY_EXTENT_U64s_MAX (BKEY_U64s + BKEY_EXTENT_VAL_U64s_MAX)
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/* Btree pointers don't carry around checksums: */
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#define BKEY_BTREE_PTR_VAL_U64s_MAX \
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((sizeof(struct bch_btree_ptr_v2) + \
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sizeof(struct bch_extent_ptr) * BCH_REPLICAS_MAX) / sizeof(__u64))
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#define BKEY_BTREE_PTR_U64s_MAX \
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(BKEY_U64s + BKEY_BTREE_PTR_VAL_U64s_MAX)
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struct bch_reservation {
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struct bch_val v;
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__le32 generation;
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__u8 nr_replicas;
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__u8 pad[3];
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} __packed __aligned(8);
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struct bch_inline_data {
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struct bch_val v;
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u8 data[];
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};
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#endif /* _BCACHEFS_EXTENTS_FORMAT_H */
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