Fixed problem with lookaheads larger than block device

Simply limiting the lookahead region to the size of
the block device fixes the problem.

Also added logic to limit the allocated region and
floor to nearest word, since the additional memory
couldn't really be used effectively.

.travis.yml

@@ -15,3 +15,4 @@ 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

lfs.c

@@ -262,12 +262,12 @@ 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.start)
+    lfs_block_t off = (((lfs_soff_t)(block - lfs->free.begin)
                 % (lfs_soff_t)(lfs->cfg->block_count))
             + lfs->cfg->block_count) % lfs->cfg->block_count;
 
-    if (off < lfs->cfg->lookahead) {
+    if (off < lfs->free.lookahead) {
-        lfs->free.lookahead[off / 32] |= 1U << (off % 32);
+        lfs->free.buffer[off / 32] |= 1U << (off % 32);
     }
 
     return 0;
@@ -285,30 +285,30 @@ 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.start + lfs->free.off == lfs->free.end) {
+            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->cfg->lookahead) {
+            if (lfs->free.off >= lfs->free.lookahead) {
                 break;
             }
 
             lfs_block_t off = lfs->free.off;
             lfs->free.off += 1;
 
-            if (!(lfs->free.lookahead[off / 32] & (1U << (off % 32)))) {
+            if (!(lfs->free.buffer[off / 32] & (1U << (off % 32)))) {
                 // found a free block
-                *block = (lfs->free.start + off) % lfs->cfg->block_count;
+                *block = (lfs->free.begin + off) % lfs->cfg->block_count;
                 return 0;
             }
         }
 
-        lfs->free.start += lfs->cfg->lookahead;
+        lfs->free.begin += lfs->free.lookahead;
         lfs->free.off = 0;
 
         // find mask of free blocks from tree
-        memset(lfs->free.lookahead, 0, lfs->cfg->lookahead/8);
+        memset(lfs->free.buffer, 0, lfs->free.lookahead/8);
         int err = lfs_traverse(lfs, lfs_alloc_lookahead, lfs);
         if (err) {
             return err;
@@ -317,7 +317,7 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
 }
 
 static void lfs_alloc_ack(lfs_t *lfs) {
-    lfs->free.end = lfs->free.start + lfs->free.off + lfs->cfg->block_count;
+    lfs->free.end = lfs->free.begin + lfs->free.off + lfs->cfg->block_count;
 }
 
 
@@ -1786,12 +1786,15 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
         }
     }
 
-    // setup lookahead
+    // 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);
     if (lfs->cfg->lookahead_buffer) {
-        lfs->free.lookahead = lfs->cfg->lookahead_buffer;
+        lfs->free.buffer = lfs->cfg->lookahead_buffer;
     } else {
-        lfs->free.lookahead = malloc(lfs->cfg->lookahead/8);
+        lfs->free.buffer = malloc(lfs->free.lookahead/8);
-        if (!lfs->free.lookahead) {
+        if (!lfs->free.buffer) {
             return LFS_ERR_NOMEM;
         }
     }
@@ -1816,7 +1819,7 @@ static int lfs_deinit(lfs_t *lfs) {
     }
 
     if (!lfs->cfg->lookahead_buffer) {
-        free(lfs->free.lookahead);
+        free(lfs->free.buffer);
     }
 
     return 0;
@@ -1829,10 +1832,10 @@ int lfs_format(lfs_t *lfs, const struct lfs_config *cfg) {
     }
 
     // create free lookahead
-    memset(lfs->free.lookahead, 0, lfs->cfg->lookahead/8);
+    memset(lfs->free.buffer, 0, lfs->free.lookahead/8);
-    lfs->free.start = 0;
+    lfs->free.begin = 0;
     lfs->free.off = 0;
-    lfs->free.end = lfs->free.start + lfs->cfg->block_count;
+    lfs->free.end = lfs->free.begin + lfs->cfg->block_count;
 
     // create superblock dir
     lfs_alloc_ack(lfs);
@@ -1908,9 +1911,9 @@ int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
     }
 
     // setup free lookahead
-    lfs->free.start = -lfs->cfg->lookahead;
+    lfs->free.begin = -lfs->free.lookahead;
-    lfs->free.off = lfs->cfg->lookahead;
+    lfs->free.off = lfs->free.lookahead;
-    lfs->free.end = lfs->free.start + lfs->cfg->block_count;
+    lfs->free.end = lfs->free.begin + lfs->cfg->block_count;
 
     // load superblock
     lfs_dir_t dir;

lfs.h

@@ -225,10 +225,11 @@ 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 start;
     lfs_block_t off;
-    uint32_t *lookahead;
+    uint32_t *buffer;
 } lfs_free_t;
 
 // The littlefs type
@@ -237,12 +238,12 @@ typedef struct lfs {
 
     lfs_block_t root[2];
     lfs_file_t *files;
-    bool deorphaned;
 
     lfs_cache_t rcache;
     lfs_cache_t pcache;
 
     lfs_free_t free;
+    bool deorphaned;
 } lfs_t;