From e611cf5050fc44acb97057654b6885ec9b060915 Mon Sep 17 00:00:00 2001 From: Christopher Haster Date: Thu, 8 Feb 2018 01:30:21 -0600 Subject: [PATCH] Fix incorrect lookahead population before ack Rather than tracking all in-flight blocks blocks during a lookahead, littlefs uses an ack scheme to mark the first allocated block that hasn't reached the disk yet. littlefs assumes all blocks since the last ack are bad or in-flight, and uses this to know when it's out of storage. However, these unacked allocations were still being populated in the lookahead buffer. If the whole block device fits in the lookahead buffer, _and_ littlefs managed to scan around the whole storage while an unacked block was still in-flight, it would assume the block was free and misallocate it. The fix is to only fill the lookahead buffer up to the last ack. The internal free structure was restructured to simplify the runtime calculation of lookahead size. --- lfs.c | 38 ++++++++++++++++++-------------------- lfs.h | 3 ++- tests/test_alloc.sh | 34 ++++++++++++++++++++++++++++++++++ 3 files changed, 54 insertions(+), 21 deletions(-) diff --git a/lfs.c b/lfs.c index b21d209..b7cc675 100644 --- a/lfs.c +++ b/lfs.c @@ -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->cfg->lookahead) { + if (off < lfs->free.size) { lfs->free.buffer[off / 32] |= 1U << (off % 32); } @@ -287,18 +287,7 @@ 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 (true) { - // check if we have looked at all blocks since last ack - if (lfs->free.begin + lfs->free.off == lfs->free.end) { - LFS_WARN("No more free space %d", lfs->free.end); - return LFS_ERR_NOSPC; - } - - if (lfs->free.off >= lfs_min( - lfs->cfg->lookahead, lfs->cfg->block_count)) { - break; - } - + while (lfs->free.off != lfs->free.size) { lfs_block_t off = lfs->free.off; lfs->free.off += 1; @@ -309,7 +298,15 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) { } } - lfs->free.begin += lfs_min(lfs->cfg->lookahead, lfs->cfg->block_count); + // 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 %d", lfs->free.off + lfs->free.begin); + 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; // find mask of free blocks from tree @@ -322,7 +319,7 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) { } static void lfs_alloc_ack(lfs_t *lfs) { - lfs->free.end = lfs->free.begin + lfs->free.off + lfs->cfg->block_count; + lfs->free.ack = lfs->free.off-1 + lfs->free.begin + lfs->cfg->block_count; } @@ -2035,11 +2032,11 @@ 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.end = lfs->free.begin + lfs->free.off + lfs->cfg->block_count; + lfs_alloc_ack(lfs); // create superblock dir - lfs_alloc_ack(lfs); lfs_dir_t superdir; err = lfs_dir_alloc(lfs, &superdir); if (err) { @@ -2112,9 +2109,10 @@ int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) { } // setup free lookahead - lfs->free.begin = -lfs_min(lfs->cfg->lookahead, lfs->cfg->block_count); - lfs->free.off = -lfs->free.begin; - lfs->free.end = lfs->free.begin + lfs->free.off + lfs->cfg->block_count; + lfs->free.begin = 0; + lfs->free.size = 0; + lfs->free.off = 0; + lfs_alloc_ack(lfs); // load superblock lfs_dir_t dir; diff --git a/lfs.h b/lfs.h index 4ce8878..e24c308 100644 --- a/lfs.h +++ b/lfs.h @@ -260,8 +260,9 @@ typedef struct lfs_superblock { typedef struct lfs_free { lfs_block_t begin; - lfs_block_t end; + lfs_block_t size; lfs_block_t off; + lfs_block_t ack; uint32_t *buffer; } lfs_free_t; diff --git a/tests/test_alloc.sh b/tests/test_alloc.sh index aaae655..493270d 100755 --- a/tests/test_alloc.sh +++ b/tests/test_alloc.sh @@ -266,6 +266,40 @@ tests/test.py << TEST lfs_mkdir(&lfs, "exhaustiondir2") => LFS_ERR_NOSPC; TEST +echo "--- Split dir test ---" +rm -rf blocks +tests/test.py << TEST + lfs_format(&lfs, &cfg) => 0; +TEST +tests/test.py << TEST + lfs_mount(&lfs, &cfg) => 0; + + // create one block whole for half a directory + lfs_file_open(&lfs, &file[0], "bump", LFS_O_WRONLY | LFS_O_CREAT) => 0; + lfs_file_write(&lfs, &file[0], (void*)"hi", 2) => 2; + lfs_file_close(&lfs, &file[0]) => 0; + + lfs_file_open(&lfs, &file[0], "exhaustion", LFS_O_WRONLY | LFS_O_CREAT); + size = strlen("blahblahblahblah"); + memcpy(buffer, "blahblahblahblah", size); + for (lfs_size_t i = 0; + i < (cfg.block_count-6)*(cfg.block_size-8); + i += size) { + lfs_file_write(&lfs, &file[0], buffer, size) => size; + } + lfs_file_close(&lfs, &file[0]) => 0; + + // open whole + lfs_remove(&lfs, "bump") => 0; + + lfs_mkdir(&lfs, "splitdir") => 0; + lfs_file_open(&lfs, &file[0], "splitdir/bump", + LFS_O_WRONLY | LFS_O_CREAT) => 0; + lfs_file_write(&lfs, &file[0], buffer, size) => LFS_ERR_NOSPC; + lfs_file_close(&lfs, &file[0]) => 0; + + lfs_unmount(&lfs) => 0; +TEST echo "--- Results ---" tests/stats.py