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Fixed issue with aggressively rounding down lookahead configuration

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The littlefs allows buffers to be passed statically in the case
that a system does not have a heap. Unfortunately, this means we
can't round up in the case of an unaligned lookahead buffer.

Double unfortunately, rounding down after clamping to the block device
size could result in a lookahead of zero for block devices < 32 blocks
large.

The assert in littlefs does catch this case, but rounding down prevents
support for < 32 block devices.

The solution is to simply require a 32-bit aligned buffer with an
assert. This avoids runtime problems while allowing a user to pass
in the correct buffer for < 32 block devices. Rounding up can be
handled at higher API levels.
This commit is contained in:
Christopher Haster
2017-11-09 19:10:08 -06:00
parent db51a395ba
commit f4aeb8331a
3 changed files with 12 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
.travis.yml
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@@ -15,7 +15,7 @@ script:
- CFLAGS="-DLFS_READ_SIZE=1 -DLFS_PROG_SIZE=1" make test
- CFLAGS="-DLFS_READ_SIZE=512 -DLFS_PROG_SIZE=512" make test
- CFLAGS="-DLFS_BLOCK_COUNT=1023" make test
- CFLAGS="-DLFS_LOOKAHEAD=2047" make test
- CFLAGS="-DLFS_LOOKAHEAD=2048" make test
# self-host with littlefs-fuse for fuzz test
- make -C littlefs-fuse

22
lfs.c
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@@ -278,7 +278,7 @@ static int lfs_alloc_lookahead(void *p, lfs_block_t block) {
% (lfs_soff_t)(lfs->cfg->block_count))
+ lfs->cfg->block_count) % lfs->cfg->block_count;
if (off < lfs->free.lookahead) {
if (off < lfs->cfg->lookahead) {
lfs->free.buffer[off / 32] |= 1U << (off % 32);
}
@@ -294,7 +294,8 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
return LFS_ERR_NOSPC;
}
if (lfs->free.off >= lfs->free.lookahead) {
if (lfs->free.off >= lfs_min(
lfs->cfg->lookahead, lfs->cfg->block_count)) {
break;
}
@@ -308,11 +309,11 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
}
}
lfs->free.begin += lfs->free.lookahead;
lfs->free.begin += lfs_min(lfs->cfg->lookahead, lfs->cfg->block_count);
lfs->free.off = 0;
// find mask of free blocks from tree
memset(lfs->free.buffer, 0, lfs->free.lookahead/8);
memset(lfs->free.buffer, 0, lfs->cfg->lookahead/8);
int err = lfs_traverse(lfs, lfs_alloc_lookahead, lfs);
if (err) {
return err;
@@ -1870,13 +1871,12 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
}
// setup lookahead, round down to nearest 32-bits
lfs->free.lookahead = lfs_min(lfs->cfg->lookahead, lfs->cfg->block_count);
lfs->free.lookahead = 32 * (lfs->free.lookahead / 32);
assert(lfs->free.lookahead > 0);
assert(lfs->cfg->lookahead % 32 == 0);
assert(lfs->cfg->lookahead > 0);
if (lfs->cfg->lookahead_buffer) {
lfs->free.buffer = lfs->cfg->lookahead_buffer;
} else {
lfs->free.buffer = malloc(lfs->free.lookahead/8);
lfs->free.buffer = malloc(lfs->cfg->lookahead/8);
if (!lfs->free.buffer) {
return LFS_ERR_NOMEM;
}
@@ -1919,7 +1919,7 @@ int lfs_format(lfs_t *lfs, const struct lfs_config *cfg) {
}
// create free lookahead
memset(lfs->free.buffer, 0, lfs->free.lookahead/8);
memset(lfs->free.buffer, 0, lfs->cfg->lookahead/8);
lfs->free.begin = 0;
lfs->free.off = 0;
lfs->free.end = lfs->free.begin + lfs->cfg->block_count;
@@ -1998,8 +1998,8 @@ int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
}
// setup free lookahead
lfs->free.begin = -lfs->free.lookahead;
lfs->free.off = lfs->free.lookahead;
lfs->free.begin = -lfs->cfg->lookahead;
lfs->free.off = lfs->cfg->lookahead;
lfs->free.end = lfs->free.begin + lfs->cfg->block_count;
// load superblock

1
lfs.h
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@@ -236,7 +236,6 @@ typedef struct lfs_superblock {
} lfs_superblock_t;
typedef struct lfs_free {
lfs_size_t lookahead;
lfs_block_t begin;
lfs_block_t end;
lfs_block_t off;