Messages in this thread | | | Date | Mon, 14 Jan 2002 12:09:59 -0600 (CST) | From | Jesse Pollard <> | Subject | Re: "dd" collapsed the loop device |
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--------- Received message begins Here ---------
> > 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?
Nope. User error....
A mounted floppy has a file system on it. The first block is boot block, super block... inode list.... ( or whatever M$ uses ).
A dd to the DEVICE starts writing at block 0. replaces the bootblock, for as many blocks as are in the file.
This, naturally, destroys the filesystem.
------------------------------------------------------------------------- Jesse I Pollard, II Email: pollard@navo.hpc.mil
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