linux/fs/bcachefs/extents_format.h
Kent Overstreet 8d52ba60c4 bcachefs: reflink_format.h
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
2024-01-21 13:27:11 -05:00

296 lines
8.2 KiB
C

/* 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 */