Re: 2.4: "access beyond end of device" after ext2 mount

[Andries Brouwer]

On Mon, Jan 17, 2005 at 05:46:35PM -0200, Marcelo Tosatti wrote:
> On Sun, Jan 16, 2005 at 12:35:30AM +0100, Mario Holbe wrote:

> > mounting an ext2 (ext3 as well) filesystem seems to modify the
> > block device's EOF behaviour: before the mount the device returned
> > EOF, after the mount it doesn't anymore:
> > 
> > [on a fresh booted system]
> > root@darkside:~# uname -a
> > Linux darkside 2.4.27 #1 Sat Jan 15 17:07:20 CET 2005 i686 GNU/Linux
> > root@darkside:~# dd if=/dev/hdg7 of=/dev/null
> > 9992366+0 records in
> > 9992366+0 records out
> > root@darkside:~# mount -t ext2 -o ro /dev/hdg7 /mnt
> > root@darkside:~# umount /dev/hdg7
> > root@darkside:~# dd if=/dev/hdg7 of=/dev/null
> > attempt to access beyond end of device
> > 22:07: rw=0, want=4996184, limit=4996183
> > dd: reading `/dev/hdg7': Input/output error
> > 9992360+0 records in
> > 9992360+0 records out
> > root@darkside:~# bc
> > 1249045 * 4
> > 4996180
> > 1249045 * 4 * 2
> > 9992360
> > 
> > Could somebody please explain this to me? Is this intentional?
> 
> No
> 
> Its indeed strange.

I suppose that what happens is the following:
mounting sets the blocksize to 4096.
After reading 9992360 sectors, reading the next block means reading
the next 8 sectors and that fails because only 6 sectors are left.

Test that this is what happens using blockdev --getbsz.

If you want to restore the device to full size, use
blockdev --setbsz 512.

Andries
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