This is a simple FUSE (Filesystem in Userspace) driver for FAT12/16/32.   It
only supports read-only mounts and does not have support for VFAT (long
filenames extension).  To compile 'fat-fuse' you need to install the
'libfuse-dev' package if it's not already installed.  To try it, do something
like:

$ cd fat-fuse
$ make
$ mkdir mnt
$ ./fat-fuse ../floppy.img mnt -o ro
$ ls -R mnt
$ cat mnt/README
$ fusermount -u mnt

The filesystem operations are defined in fat_fuse_ops.c.  They rely on code in
fat_volume.c and fat_file.c.

Other notes about the fat-fuse program:

* The file allocation table is mapped into memory with mmap().  Other data in
  the filesystem, such as cluster data, are read with pread().

* Whenever the child of a directory is needed, all children are read at the same
  time and inserted into a balanced binary tree of that directory's children,
  sorted by name (including extension, if present).  The children of a directory
  are freed at a later time if they are no longer in use and the number of
  allocated files has exceeded a soft limit.

* Whenever a file with no current open file descriptors is opened, a table is
  allocated to map cluster indices of that file to actual clusters.  When a read
  at a given offset is requested, all previous entries in the table up until the
  entry needed to complete the read are read from the FAT.  When a file is
  closed for the last time, its table of clusters is freed.

* The filesystem code is not thread-safe, so concurrent filesystem operations
  will be serialized.

* The filesystem code does not try to detect cyclic directory structures (which
  are possible in FAT).  It will just recurse indefinitely.