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reftable/block: store block pointer in the block iterator

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The block iterator requires access to a bunch of data from the
underlying `reftable_block` that it is iterating over. This data is
stored by copying over relevant data into a separate set of variables.
This has multiple downsides:

  - We require more storage space than necessary. This is more of a
    theoretical issue as we shouldn't ever have many blocks.

  - We have to perform more bookkeeping, and the variable names are
    inconsistent across the two data structures. This can lead to some
    confusion.

  - The lifetime of the block iterator is tied to the block anyway, but
    we hide that a bit by only storing pointers pointing into the block.

There isn't really any good reason why we rip out parts of the block
instead of storing a pointer to the block itself.

Refactor the code to do so. Despite being simpler, it also allows us to
decouple the lifetime of the block iterator from seeking in a subsequent
commit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Patrick Steinhardt
2025-04-07 15:16:22 +02:00
committed by Junio C Hamano
parent 655e18d6b4
commit 156d79cef0
2 changed files with 9 additions and 17 deletions
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22
reftable/block.c
View File

@@ -381,13 +381,11 @@ static uint32_t block_restart_offset(const struct reftable_block *b, size_t idx)
return reftable_get_be24(b->block_data.data + b->restart_off + 3 * idx);
}
void block_iter_seek_start(struct block_iter *it, const struct reftable_block *b)
void block_iter_seek_start(struct block_iter *it, const struct reftable_block *block)
{
it->block = b->block_data.data;
it->block_len = b->restart_off;
it->hash_size = b->hash_size;
it->block = block;
reftable_buf_reset(&it->last_key);
it->next_off = b->header_off + 4;
it->next_off = block->header_off + 4;
}
struct restart_needle_less_args {
@@ -435,14 +433,14 @@ static int restart_needle_less(size_t idx, void *_args)
int block_iter_next(struct block_iter *it, struct reftable_record *rec)
{
struct string_view in = {
.buf = (unsigned char *) it->block + it->next_off,
.len = it->block_len - it->next_off,
.buf = (unsigned char *) it->block->block_data.data + it->next_off,
.len = it->block->restart_off - it->next_off,
};
struct string_view start = in;
uint8_t extra = 0;
int n = 0;
if (it->next_off >= it->block_len)
if (it->next_off >= it->block->restart_off)
return 1;
n = reftable_decode_key(&it->last_key, &extra, in);
@@ -452,7 +450,7 @@ int block_iter_next(struct block_iter *it, struct reftable_record *rec)
return REFTABLE_FORMAT_ERROR;
string_view_consume(&in, n);
n = reftable_record_decode(rec, it->last_key, extra, in, it->hash_size,
n = reftable_record_decode(rec, it->last_key, extra, in, it->block->hash_size,
&it->scratch);
if (n < 0)
return -1;
@@ -467,8 +465,6 @@ void block_iter_reset(struct block_iter *it)
reftable_buf_reset(&it->last_key);
it->next_off = 0;
it->block = NULL;
it->block_len = 0;
it->hash_size = 0;
}
void block_iter_close(struct block_iter *it)
@@ -528,9 +524,7 @@ int block_iter_seek_key(struct block_iter *it, const struct reftable_block *bloc
it->next_off = block_restart_offset(block, i - 1);
else
it->next_off = block->header_off + 4;
it->block = block->block_data.data;
it->block_len = block->restart_off;
it->hash_size = block->hash_size;
it->block = block;
err = reftable_record_init(&rec, reftable_block_type(block));
if (err < 0)

4
reftable/block.h
View File

@@ -67,9 +67,7 @@ void block_writer_release(struct block_writer *bw);
struct block_iter {
/* offset within the block of the next entry to read. */
uint32_t next_off;
const unsigned char *block;
size_t block_len;
uint32_t hash_size;
const struct reftable_block *block;
/* key for last entry we read. */
struct reftable_buf last_key;