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Diffstat (limited to 'fs/bcachefs/extents_format.h')
| -rw-r--r-- | fs/bcachefs/extents_format.h | 295 |
1 files changed, 295 insertions, 0 deletions
diff --git a/fs/bcachefs/extents_format.h b/fs/bcachefs/extents_format.h new file mode 100644 index 0000000000..3bd2fdbb08 --- /dev/null +++ b/fs/bcachefs/extents_format.h @@ -0,0 +1,295 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _BCACHEFS_EXTENTS_FORMAT_H +#define _BCACHEFS_EXTENTS_FORMAT_H + +/* + * In extent bkeys, the value is a list of pointers (bch_extent_ptr), optionally + * preceded by checksum/compression information (bch_extent_crc32 or + * bch_extent_crc64). + * + * One major determining factor in the format of extents is how we handle and + * represent extents that have been partially overwritten and thus trimmed: + * + * If an extent is not checksummed or compressed, when the extent is trimmed we + * don't have to remember the extent we originally allocated and wrote: we can + * merely adjust ptr->offset to point to the start of the data that is currently + * live. The size field in struct bkey records the current (live) size of the + * extent, and is also used to mean "size of region on disk that we point to" in + * this case. + * + * Thus an extent that is not checksummed or compressed will consist only of a + * list of bch_extent_ptrs, with none of the fields in + * bch_extent_crc32/bch_extent_crc64. + * + * When an extent is checksummed or compressed, it's not possible to read only + * the data that is currently live: we have to read the entire extent that was + * originally written, and then return only the part of the extent that is + * currently live. + * + * Thus, in addition to the current size of the extent in struct bkey, we need + * to store the size of the originally allocated space - this is the + * compressed_size and uncompressed_size fields in bch_extent_crc32/64. Also, + * when the extent is trimmed, instead of modifying the offset field of the + * pointer, we keep a second smaller offset field - "offset into the original + * extent of the currently live region". + * + * The other major determining factor is replication and data migration: + * + * Each pointer may have its own bch_extent_crc32/64. When doing a replicated + * write, we will initially write all the replicas in the same format, with the + * same checksum type and compression format - however, when copygc runs later (or + * tiering/cache promotion, anything that moves data), it is not in general + * going to rewrite all the pointers at once - one of the replicas may be in a + * bucket on one device that has very little fragmentation while another lives + * in a bucket that has become heavily fragmented, and thus is being rewritten + * sooner than the rest. + * + * Thus it will only move a subset of the pointers (or in the case of + * tiering/cache promotion perhaps add a single pointer without dropping any + * current pointers), and if the extent has been partially overwritten it must + * write only the currently live portion (or copygc would not be able to reduce + * fragmentation!) - which necessitates a different bch_extent_crc format for + * the new pointer. + * + * But in the interests of space efficiency, we don't want to store one + * bch_extent_crc for each pointer if we don't have to. + * + * Thus, a bch_extent consists of bch_extent_crc32s, bch_extent_crc64s, and + * bch_extent_ptrs appended arbitrarily one after the other. We determine the + * type of a given entry with a scheme similar to utf8 (except we're encoding a + * type, not a size), encoding the type in the position of the first set bit: + * + * bch_extent_crc32 - 0b1 + * bch_extent_ptr - 0b10 + * bch_extent_crc64 - 0b100 + * + * We do it this way because bch_extent_crc32 is _very_ constrained on bits (and + * bch_extent_crc64 is the least constrained). + * + * Then, each bch_extent_crc32/64 applies to the pointers that follow after it, + * until the next bch_extent_crc32/64. + * + * If there are no bch_extent_crcs preceding a bch_extent_ptr, then that pointer + * is neither checksummed nor compressed. + */ + +#define BCH_EXTENT_ENTRY_TYPES() \ + x(ptr, 0) \ + x(crc32, 1) \ + x(crc64, 2) \ + x(crc128, 3) \ + x(stripe_ptr, 4) \ + x(rebalance, 5) +#define BCH_EXTENT_ENTRY_MAX 6 + +enum bch_extent_entry_type { +#define x(f, n) BCH_EXTENT_ENTRY_##f = n, + BCH_EXTENT_ENTRY_TYPES() +#undef x +}; + +/* Compressed/uncompressed size are stored biased by 1: */ +struct bch_extent_crc32 { +#if defined(__LITTLE_ENDIAN_BITFIELD) + __u32 type:2, + _compressed_size:7, + _uncompressed_size:7, + offset:7, + _unused:1, + csum_type:4, + compression_type:4; + __u32 csum; +#elif defined (__BIG_ENDIAN_BITFIELD) + __u32 csum; + __u32 compression_type:4, + csum_type:4, + _unused:1, + offset:7, + _uncompressed_size:7, + _compressed_size:7, + type:2; +#endif +} __packed __aligned(8); + +#define CRC32_SIZE_MAX (1U << 7) +#define CRC32_NONCE_MAX 0 + +struct bch_extent_crc64 { +#if defined(__LITTLE_ENDIAN_BITFIELD) + __u64 type:3, + _compressed_size:9, + _uncompressed_size:9, + offset:9, + nonce:10, + csum_type:4, + compression_type:4, + csum_hi:16; +#elif defined (__BIG_ENDIAN_BITFIELD) + __u64 csum_hi:16, + compression_type:4, + csum_type:4, + nonce:10, + offset:9, + _uncompressed_size:9, + _compressed_size:9, + type:3; +#endif + __u64 csum_lo; +} __packed __aligned(8); + +#define CRC64_SIZE_MAX (1U << 9) +#define CRC64_NONCE_MAX ((1U << 10) - 1) + +struct bch_extent_crc128 { +#if defined(__LITTLE_ENDIAN_BITFIELD) + __u64 type:4, + _compressed_size:13, + _uncompressed_size:13, + offset:13, + nonce:13, + csum_type:4, + compression_type:4; +#elif defined (__BIG_ENDIAN_BITFIELD) + __u64 compression_type:4, + csum_type:4, + nonce:13, + offset:13, + _uncompressed_size:13, + _compressed_size:13, + type:4; +#endif + struct bch_csum csum; +} __packed __aligned(8); + +#define CRC128_SIZE_MAX (1U << 13) +#define CRC128_NONCE_MAX ((1U << 13) - 1) + +/* + * @reservation - pointer hasn't been written to, just reserved + */ +struct bch_extent_ptr { +#if defined(__LITTLE_ENDIAN_BITFIELD) + __u64 type:1, + cached:1, + unused:1, + unwritten:1, + offset:44, /* 8 petabytes */ + dev:8, + gen:8; +#elif defined (__BIG_ENDIAN_BITFIELD) + __u64 gen:8, + dev:8, + offset:44, + unwritten:1, + unused:1, + cached:1, + type:1; +#endif +} __packed __aligned(8); + +struct bch_extent_stripe_ptr { +#if defined(__LITTLE_ENDIAN_BITFIELD) + __u64 type:5, + block:8, + redundancy:4, + idx:47; +#elif defined (__BIG_ENDIAN_BITFIELD) + __u64 idx:47, + redundancy:4, + block:8, + type:5; +#endif +}; + +struct bch_extent_rebalance { +#if defined(__LITTLE_ENDIAN_BITFIELD) + __u64 type:6, + unused:34, + compression:8, /* enum bch_compression_opt */ + target:16; +#elif defined (__BIG_ENDIAN_BITFIELD) + __u64 target:16, + compression:8, + unused:34, + type:6; +#endif +}; + +union bch_extent_entry { +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ || __BITS_PER_LONG == 64 + unsigned long type; +#elif __BITS_PER_LONG == 32 + struct { + unsigned long pad; + unsigned long type; + }; +#else +#error edit for your odd byteorder. +#endif + +#define x(f, n) struct bch_extent_##f f; + BCH_EXTENT_ENTRY_TYPES() +#undef x +}; + +struct bch_btree_ptr { + struct bch_val v; + + __u64 _data[0]; + struct bch_extent_ptr start[]; +} __packed __aligned(8); + +struct bch_btree_ptr_v2 { + struct bch_val v; + + __u64 mem_ptr; + __le64 seq; + __le16 sectors_written; + __le16 flags; + struct bpos min_key; + __u64 _data[0]; + struct bch_extent_ptr start[]; +} __packed __aligned(8); + +LE16_BITMASK(BTREE_PTR_RANGE_UPDATED, struct bch_btree_ptr_v2, flags, 0, 1); + +struct bch_extent { + struct bch_val v; + + __u64 _data[0]; + union bch_extent_entry start[]; +} __packed __aligned(8); + +/* Maximum size (in u64s) a single pointer could be: */ +#define BKEY_EXTENT_PTR_U64s_MAX\ + ((sizeof(struct bch_extent_crc128) + \ + sizeof(struct bch_extent_ptr)) / sizeof(__u64)) + +/* Maximum possible size of an entire extent value: */ +#define BKEY_EXTENT_VAL_U64s_MAX \ + (1 + BKEY_EXTENT_PTR_U64s_MAX * (BCH_REPLICAS_MAX + 1)) + +/* * Maximum possible size of an entire extent, key + value: */ +#define BKEY_EXTENT_U64s_MAX (BKEY_U64s + BKEY_EXTENT_VAL_U64s_MAX) + +/* Btree pointers don't carry around checksums: */ +#define BKEY_BTREE_PTR_VAL_U64s_MAX \ + ((sizeof(struct bch_btree_ptr_v2) + \ + sizeof(struct bch_extent_ptr) * BCH_REPLICAS_MAX) / sizeof(__u64)) +#define BKEY_BTREE_PTR_U64s_MAX \ + (BKEY_U64s + BKEY_BTREE_PTR_VAL_U64s_MAX) + +struct bch_reservation { + struct bch_val v; + + __le32 generation; + __u8 nr_replicas; + __u8 pad[3]; +} __packed __aligned(8); + +struct bch_inline_data { + struct bch_val v; + u8 data[]; +}; + +#endif /* _BCACHEFS_EXTENTS_FORMAT_H */ |