This was a pretty simple oversight on my part. Conceptually, there's no
difference between lfs_fs_getattr and lfs_getattr("/"). Any operations
on directories can be applied "globally" by referring to the root
directory.
Implementation wise, this actually fixes the "corner case" of storing
attributes on the root directory, which is broken since the root
directory doesn't have a related entry. Instead we need to use the root
superblock for this purpose.
Fewer functions means less code to document and maintain, so this is a
nice benefit. Now we just have a single lfs_getattr/setattr/removeattr set
of functions along with the ability to access attributes atomically in
lfs_file_opencfg.
Because of limitations in how littlefs manages attributes on disk,
littlefs views zero-length attributes and missing attributes as the same
thing. The simpliest implementation of attributes mirrors this behaviour
transparently for the user.
Now that littlefs has been rebuilt almost from the ground up with the
intention to support custom attributes, adding in custom attribute
support is relatively easy.
The highest bit in the 9-bit type structure indicates that an attribute
is a user-specified custom attribute. The user then has a full 8-bits to
specify the attribute type. Other than that, custom attributes are
treated the same as system-level attributes.
Also made some tweaks to custom attributes:
- Adopted the opencfg for file-level attributes provided by dpgeorge
- Changed setattrs/getattrs to the simpler setattr/getattr functions
users will probably be more familiar with. Note that multiple
attributes can still be committed atomically with files, though not
with directories.
- Changed LFS_ATTRS_MAX -> LFS_ATTR_MAX since there's no longer a global
limit on the sum of attribute sizes, which was rather confusing.
Though they are still limited by what can fit in a metadata-pair.
