There is preliminary FAT support for ELKS available now. This is based on old Linux
drivers ported to ELKS by a Chinese developer called Zouys. I made these sources work
with the current ELKS version and fixed a few problems.

To enable the FAT support run "make menuconfig" in the elks directory. Then enable
"MS-DOS file system" and "Full VFS support" in the "Filesystem Support" section. Disable
e.g. the serial device drivers to get sufficient memory space. Then run the build.sh
script.

In the elkscmd/test/fat directory there is a script to generate a fat32 disk image which
I have used for testing. The is also a script to list the contents of this disk image.
After you have generated a FAT disk image, you can run the qemu.sh script which allows
to run ELKS with Qemu from the elkscmd/test/fat directory.

If you run ELKS with this script, ELKS will report a floppy disk and a hard disk. The
etc/rc.sysint script will try to mount the disk if a bda1 device is present. You can
also mount the FAT32 hard disk from the command line with the command:
"mount -t msdos /dev/bda1 /mnt".
Then you can enter ls /mnt to list the files and directories in the root directory of the
FAT32 disk.

A FAT12 floppy image can be mounted with: "mount -t msdos /dev/fd1 /mnt". In the qemu.sh
script you have to specify the floppy image e.g. with:
"qemu-system-i386 -fda elkscmd/full3 -fdb ./fddos"

The FAT support allows to read data from disks formatted in the FAT32 or FAT12 format
and list the files on these disks. You can also write back a modified file and extend
its size. You can generate new files too.

You can also access USB flash disks from Qemu and read files from that. I formated a
flash disk with a 480 MB partition as number one and could read a file from that using
ELKS and the FAT32 support.

The mv command will only work if one of the specified files is on a minix disk. You
cannot move a file just on a FAT disk. Also rm and ln do not work.

Currently, FAT16 is not supported. The reason is that you cannot list the files
on the FAT16 disk since the readdir command will hang in map_buffer() in fs/buffer.c.
It hangs with the message: "BUFMAP: buffer #x waiting on L1 slot\n".
You could open files if you knew their names in advance.

In the elkscmd/test/fat directory there is a script to generate a fat32 disk image which
I have used for testing. The is also a script to list the contents of this disk image and a
qemu.sh script which allows to run ELKS with Qemu from this directory.

A FAT12 floppy image can be mounted with: "mount -t msdos /dev/fd1 /mnt". In the qemu.sh
script you have to specify the floppy image e.g. with:
"qemu-system-i386 -fda elkscmd/full3 -fdb ./fddos"

The code contains long file name support but "ls" will still report the files as "xxx~1" and
you have to use this file name to open the files.

There is still a lot of testing and debugging required for this file system, but it can be
used now to transfer files to and from FAT disks to ELKS. I hope other developers will be able
to fix some of these issues.

8th April 2017 Georg Potthast