Fixed issue with creating files named "littlefs"

A rather humorous issue, we accidentally ended up mixing our file
namespace with our superblocks. This meant if we created a file named
"littlefs" it would reference the superblock and all sorts of things
would break.

Fixing this also highlighted another issue, the fact that the superblock
always needs to come before any file entries in the directory. I didn't
account for this in the initial B-tree design, but we need a higher
ordering for superblocks + children + files than just name. To fix this
I added ordering information in the 2 bits currently unused in the tag
type. Though note that the size of these fields are flexible.

9-bit type field:
[---      9      ---]
[1|- 3 -|- 2 -|- 3 -]
 ^   ^     ^     ^- type-specific info
 |   |     \------- ordering info
 |   \------------- subtype
 \----------------- user bit

tests/debug.py

@@ -4,8 +4,8 @@ import struct
 import binascii
 
 TYPES = {
-    (0x1ff, 0x002): 'reg',
-    (0x1ff, 0x003): 'dir',
+    (0x1ff, 0x011): 'create reg',
+    (0x1ff, 0x010): 'create dir',
     (0x1ff, 0x001): 'superblock',
     (0x1ff, 0x020): 'delete',
     (0x1f0, 0x0e0): 'globals',
@@ -23,10 +23,10 @@ def typeof(type):
         mask = 0x1ff & ~((1 << prefix)-1)
         if (mask, type & mask) in TYPES:
             return TYPES[mask, type & mask] + (
-                ' [%0*x]' % (prefix/4, type & ((1 << prefix)-1))
+                ' %0*x' % (prefix/4, type & ((1 << prefix)-1))
                 if prefix else '')
     else:
-        return '[%02x]' % type
+        return '%02x' % type
 
 def main(*blocks):
     # find most recent block

tests/test_paths.sh

@@ -139,6 +139,14 @@ tests/test.py << TEST
     lfs_unmount(&lfs) => 0;
 TEST
 
+echo "--- Superblock conflict test ---"
+tests/test.py << TEST
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_mkdir(&lfs, "littlefs") => 0;
+    lfs_remove(&lfs, "littlefs") => 0;
+    lfs_unmount(&lfs) => 0;
+TEST
+
 echo "--- Max path test ---"
 tests/test.py << TEST
     lfs_mount(&lfs, &cfg) => 0;