"dd" collapsed the loop device

[Michael Zhu]

Hello,everyone,I have a problem when I used the loop
device. I don't know whether is a loop device bug. I
used the following commands to connect the loop device
with the floppy disk device.

losetup -e xor /dev/loop0 /dev/fd0
mke2fs /dev/loop0
mount /dev/loop0 /floppy

Then I copy something to the floppy and read it back.
Everything is OK. It works perfectly. 

The problem was happened when I try to copy something
directly from the /dev/fd0. I use the following
demand.

dd if=test.c of=/dev/fd0

The output of the upper command is:
50+1 records in
50+1 records out

Then I used the "ls /floppy". I found nothing copied
to the floppy. Then I used "umount /floppy" to umount
the floppy disk device. After that I used the
following command to try to mount the floppy disk
again.

mount /dev/loop0 /floppy

It returned an error. Say:

mount: wrong fs type. bad option. bad superblock on
/dev/loop0. or too many mounted file systems

It seemed that the "dd if=test.c of=/dev/fd0"
corrupted the data on the floppy disk. What is wrong?
What happened to the floppy disk? Is it a bug of the
loop device?

Thanks

Michael

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