Originally, prepend_drive_to_path was designed to be a macro, and it
modified local path variables to point to a temporary buffers.
When it was converted into a function, modification to path variables
were no longer visible outside of this function.
In addition to that, prepend_drive_to_path allocated 2k bytes on the
stack for temporary path buffers. This is replaced with path buffers
allocated as part of vfs_fat context object. Locking is added around
parts of code which use these temporary buffers.
Additionally, _lock member of vfs_fat_ctx_t was placed after the
variable-sized files array, which caused the first entry in the
array to be never used. This change fixes the order of members
and adds comments.
1a73b41b10