Previously, the VFS layer would try to handle renames more-or-less by
itself, which really only worked for ext2, and even that was only due to
the replace_child kludge existing specifically for this purpose. This
never worked properly for FATFS, since the VFS layer effectively
depended on filesystems having some kind of reference-counting for
inodes, which is something that simply doesn't exist on any FAT variant
we support.
To resolve various issues with the existing scheme, this commit makes
filesystem implementations themselves responsible for the actual rename
operation, while keeping all the existing validation inside the VFS
layer. The only intended behavior change here is that rename operations
should actually properly work on FATFS.
Such operation is almost equivalent to writing on an Inode, so lock the
Inode m_inode_lock exclusively.
All FileSystem Inode implementations then override a new method called
truncate_locked which should implement the actual truncating.
Because the ".." entry in a directory is a separate inode, if a
directory is renamed to a new location, then we should update this entry
the point to the new parent directory as well.
Co-authored-by: Liav A <liavalb@gmail.com>
