Fixed name ordering when names only differ in length

Wild this hasn't been caught until now.

Because the exact ordering of the comparison in lfs_bd_cmp is a bit
ambiguous, lfs_dir_find_match returned the wrong result when filenames
were equal, and only differed in length.

For example:

  - cmp("a", "aa") should be LFS_CMP_LT
  - cmp("aaa", "aa") should be LFS_CMP_GT

We're quite lucky that none of the littlefs internals currently depend
on the sorted order, otherwise we'd probably be stuck with this weird
ordering for backwards compatibility reasons...

Fixed, and added some test cases over directory ordering to prevent
regression in the future.

Found by andriyndev

.github/workflows/release.yml

@@ -112,7 +112,7 @@ jobs:
             table[$i,$j]=$c_camel
             ((j+=1))
 
-            for s in code stack struct
+            for s in code stack structs
             do
               f=sizes/thumb${c:+-$c}.$s.csv
               [ -e $f ] && table[$i,$j]=$( \

DESIGN.md

@@ -59,7 +59,7 @@ This leaves us with three major requirements for an embedded filesystem.
    RAM to temporarily store filesystem metadata.
 
    For ROM, this means we need to keep our design simple and reuse code paths
-   were possible. For RAM we have a stronger requirement, all RAM usage is
+   where possible. For RAM we have a stronger requirement, all RAM usage is
    bounded. This means RAM usage does not grow as the filesystem changes in
    size or number of files. This creates a unique challenge as even presumably
    simple operations, such as traversing the filesystem, become surprisingly
@@ -626,7 +626,7 @@ log₂_n_ pointers that skip to different preceding elements of the
 skip-list.
 
 The name comes from heavy use of the [CTZ instruction][wikipedia-ctz], which
-lets us calculate the power-of-two factors efficiently. For a give block _n_,
+lets us calculate the power-of-two factors efficiently. For a given block _n_,
 that block contains ctz(_n_)+1 pointers.
 
 ```

lfs.c

@@ -1430,8 +1430,8 @@ static int lfs_dir_find_match(void *data,
     }
 
     // only equal if our size is still the same
-    if (name->size != lfs_tag_size(tag)) {
-        return (name->size < lfs_tag_size(tag)) ? LFS_CMP_LT : LFS_CMP_GT;
+    if (lfs_tag_size(tag) != name->size) {
+        return (lfs_tag_size(tag) < name->size) ? LFS_CMP_LT : LFS_CMP_GT;
     }
 
     // found a match!
@@ -2151,9 +2151,11 @@ static int lfs_dir_splittingcompact(lfs_t *lfs, lfs_mdir_t *dir,
             return size;
         }
 
-        // do we have extra space? littlefs can't reclaim this space
-        // by itself, so expand cautiously
-        if ((lfs_size_t)size < lfs->block_count/2) {
+        // littlefs cannot reclaim expanded superblocks, so expand cautiously
+        //
+        // if our filesystem is more than ~88% full, don't expand, this is
+        // somewhat arbitrary
+        if (lfs->block_count - size > lfs->block_count/8) {
             LFS_DEBUG("Expanding superblock at rev %"PRIu32, dir->rev);
             int err = lfs_dir_split(lfs, dir, attrs, attrcount,
                     source, begin, end);

tests/test_dirs.toml

@@ -717,6 +717,105 @@ code = '''
     lfs_unmount(&lfs) => 0;
 '''
 
+# littlefs should keep directories in lexicographic order
+[cases.test_dirs_ordering]
+# ORDER=0 => inorder
+# ORDER=1 => reversed
+# ORDER=2 => random
+defines.ORDER = [0, 1, 2]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+    lfs_mount(&lfs, cfg) => 0;
+    if (ORDER == 0) {
+        lfs_mkdir(&lfs, "a") => 0;
+        lfs_mkdir(&lfs, "b") => 0;
+        lfs_mkdir(&lfs, "c") => 0;
+    } else if (ORDER == 1) {
+        lfs_mkdir(&lfs, "c") => 0;
+        lfs_mkdir(&lfs, "b") => 0;
+        lfs_mkdir(&lfs, "a") => 0;
+    } else if (ORDER == 2) {
+        // "random"
+        lfs_mkdir(&lfs, "a") => 0;
+        lfs_mkdir(&lfs, "c") => 0;
+        lfs_mkdir(&lfs, "b") => 0;
+    }
+
+    // check the order
+    lfs_dir_t dir;
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    struct lfs_info info;
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, ".") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "..") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "a") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "b") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "c") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+
+    lfs_unmount(&lfs) => 0;
+'''
+
+[cases.test_dirs_ordering_length]
+# ORDER=0 => inorder
+# ORDER=1 => reversed
+# ORDER=2 => random
+defines.ORDER = [0, 1, 2]
+code = '''
+    lfs_t lfs;
+    lfs_format(&lfs, cfg) => 0;
+    lfs_mount(&lfs, cfg) => 0;
+    if (ORDER == 0) {
+        lfs_mkdir(&lfs, "a") => 0;
+        lfs_mkdir(&lfs, "aa") => 0;
+        lfs_mkdir(&lfs, "aaa") => 0;
+    } else if (ORDER == 1) {
+        lfs_mkdir(&lfs, "aaa") => 0;
+        lfs_mkdir(&lfs, "aa") => 0;
+        lfs_mkdir(&lfs, "a") => 0;
+    } else if (ORDER == 2) {
+        // "random"
+        lfs_mkdir(&lfs, "a") => 0;
+        lfs_mkdir(&lfs, "aaa") => 0;
+        lfs_mkdir(&lfs, "aa") => 0;
+    }
+
+    // check the order
+    lfs_dir_t dir;
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    struct lfs_info info;
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, ".") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "..") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "a") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "aa") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "aaa") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+
+    lfs_unmount(&lfs) => 0;
+'''
+
 [cases.test_dirs_other_errors]
 code = '''
     lfs_t lfs;