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Relaxed lookahead buffer alignment

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This drops the lookahead buffer from operating on 32-bit words to
operating on 8-bit bytes, and removes any alignment requirement. This
may have some minor performance impact, but it is unlikely to be
significant when you consider IO overhead.

The original motivation for 32-bit alignment was an attempt at
future-proofing in case we wanted some more complex on-disk data
structure. This never happened, and even if it did, it could have been
added via additional config options.

This has been a significant pain point for users, since providing
word-aligned byte-sized buffers in C can be a bit annoying.
This commit is contained in:
Christopher Haster
2023-12-20 00:32:17 -06:00
parent 1f9c3c04b1
commit b1b10c0e75
2 changed files with 11 additions and 13 deletions
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9
lfs.h
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@@ -226,7 +226,7 @@ struct lfs_config {
// Size of the lookahead buffer in bytes. A larger lookahead buffer
// increases the number of blocks found during an allocation pass. The
// lookahead buffer is stored as a compact bitmap, so each byte of RAM
// can track 8 blocks. Must be a multiple of 8.
// can track 8 blocks.
lfs_size_t lookahead_size;
// Optional statically allocated read buffer. Must be cache_size.
@@ -237,9 +237,8 @@ struct lfs_config {
// By default lfs_malloc is used to allocate this buffer.
void *prog_buffer;
// Optional statically allocated lookahead buffer. Must be lookahead_size
// and aligned to a 32-bit boundary. By default lfs_malloc is used to
// allocate this buffer.
// Optional statically allocated lookahead buffer. Must be lookahead_size.
// By default lfs_malloc is used to allocate this buffer.
void *lookahead_buffer;
// Optional upper limit on length of file names in bytes. No downside for
@@ -435,7 +434,7 @@ typedef struct lfs {
lfs_block_t size;
lfs_block_t next;
lfs_block_t ckpoint;
uint32_t *buffer;
uint8_t *buffer;
} lookahead;
const struct lfs_config *cfg;