Messages in this thread | | | Date | Mon, 14 Jan 2002 11:18:43 -0700 | From | Andreas Dilger <> | Subject | Re: "dd" collapsed the loop device |
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On Jan 14, 2002 12:54 -0500, Michael Zhu wrote: > Hello,everyone,I have a problem when I used the loop > device. I don't know whether is a loop device bug.
User 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.
Great.
> 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.
Well, this is wrong for several reasons: 1) don't access /dev/fd0 when you use it via loopback, use /dev/loop0 2) don't use "dd" to copy a file, use "cp" 3) don't write into the device, but the filesystem instead: cp test.c /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?
Because test.c is not a filesystem, and you have overwritten the filesystem on /dev/fd0 with junk. This is not a bug in the loop driver.
Cheers, Andreas -- Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/
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