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littlefs: Fixed lookahead overflow and removed unbounded lookahead pointers 

As pointed out by davidefer, the lookahead pointer modular arithmetic
does not work around integer overflow when the pointer size is not a
multiple of the block count.

To avoid overflow problems, the easy solution is to stop trying to
work around integer overflows and keep the lookahead offset inside the
block device. To make this work, the ack was modified into a resetable
counter that is decremented every block allocation.

As a plus, quite a bit of the allocation logic ended up simplified.
pull/6604/head
Christopher Haster 2018-04-10 15:14:27 -05:00
parent 47bee2343c
commit 9e03b24120
2 changed files with 24 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
features/filesystem/littlefs/littlefs/lfs.c
View File

@ -270,8 +270,7 @@ int lfs_deorphan(lfs_t *lfs);
static int lfs_alloc_lookahead(void *p, lfs_block_t block) {
lfs_t *lfs = p;
lfs_block_t off = (((lfs_soff_t)(block - lfs->free.begin)
% (lfs_soff_t)(lfs->cfg->block_count))
lfs_block_t off = ((block - lfs->free.off)
+ lfs->cfg->block_count) % lfs->cfg->block_count;
if (off < lfs->free.size) {
@ -283,20 +282,22 @@ static int lfs_alloc_lookahead(void *p, lfs_block_t block) {
static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
while (true) {
while (lfs->free.off != lfs->free.size) {
lfs_block_t off = lfs->free.off;
lfs->free.off += 1;
while (lfs->free.index != lfs->free.size) {
lfs_block_t off = lfs->free.index;
lfs->free.index += 1;
lfs->free.ack -= 1;
if (!(lfs->free.buffer[off / 32] & (1U << (off % 32)))) {
// found a free block
*block = (lfs->free.begin + off) % lfs->cfg->block_count;
*block = (lfs->free.off + off) % lfs->cfg->block_count;
// eagerly find next off so an alloc ack can
// discredit old lookahead blocks
while (lfs->free.off != lfs->free.size &&
(lfs->free.buffer[lfs->free.off / 32] &
(1U << (lfs->free.off % 32)))) {
lfs->free.off += 1;
while (lfs->free.index != lfs->free.size &&
(lfs->free.buffer[lfs->free.index / 32]
& (1U << (lfs->free.index % 32)))) {
lfs->free.index += 1;
lfs->free.ack -= 1;
}
return 0;
@ -304,15 +305,15 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
}
// check if we have looked at all blocks since last ack
if (lfs->free.off == lfs->free.ack - lfs->free.begin) {
LFS_WARN("No more free space %ld", lfs->free.off + lfs->free.begin);
if (lfs->free.ack == 0) {
LFS_WARN("No more free space %ld", lfs->free.index+lfs->free.off);
return LFS_ERR_NOSPC;
}
lfs->free.begin += lfs->free.size;
lfs->free.size = lfs_min(lfs->cfg->lookahead,
lfs->free.ack - lfs->free.begin);
lfs->free.off = 0;
lfs->free.off = (lfs->free.off + lfs->free.size)
% lfs->cfg->block_count;
lfs->free.size = lfs_min(lfs->cfg->lookahead, lfs->free.ack);
lfs->free.index = 0;
// find mask of free blocks from tree
memset(lfs->free.buffer, 0, lfs->cfg->lookahead/8);
@ -324,7 +325,7 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
}
static void lfs_alloc_ack(lfs_t *lfs) {
lfs->free.ack = lfs->free.begin+lfs->free.off + lfs->cfg->block_count;
lfs->free.ack = lfs->cfg->block_count;
}
@ -2103,9 +2104,9 @@ int lfs_format(lfs_t *lfs, const struct lfs_config *cfg) {
// create free lookahead
memset(lfs->free.buffer, 0, lfs->cfg->lookahead/8);
lfs->free.begin = 0;
lfs->free.size = lfs_min(lfs->cfg->lookahead, lfs->cfg->block_count);
lfs->free.off = 0;
lfs->free.size = lfs_min(lfs->cfg->lookahead, lfs->cfg->block_count);
lfs->free.index = 0;
lfs_alloc_ack(lfs);
// create superblock dir
@ -2182,9 +2183,9 @@ int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
}
// setup free lookahead
lfs->free.begin = 0;
lfs->free.size = 0;
lfs->free.off = 0;
lfs->free.size = 0;
lfs->free.index = 0;
lfs_alloc_ack(lfs);
// load superblock

4
features/filesystem/littlefs/littlefs/lfs.h
View File

@ -259,9 +259,9 @@ typedef struct lfs_superblock {
} lfs_superblock_t;
typedef struct lfs_free {
lfs_block_t begin;
lfs_block_t size;
lfs_block_t off;
lfs_block_t size;
lfs_block_t index;
lfs_block_t ack;
uint32_t *buffer;
} lfs_free_t;