On Tue, May 23, 2017 at 11:41:52AM -0400, Theodore Ts'o wrote:

On Tue, May 23, 2017 at 12:20:59AM +0100, Marc Thomas wrote:

quoted

Hi All,

Would you agree this is a bug? As I understand it, reading from an
"unpopulated" region of a sparse file should return all zeros - so the
md5sum should be the same before and after migration.

I agree that sparse files should be properly handled after bmap2extent
conversion.  This code hasn't received that much use or testing, but
I've tried to replicate the problem and I haven't succeeded.  This
script works for me:

----- cut here -----
#!/bin/bash

rm -f /tmp/foo.img
mke2fs -t ext3 -Fq /tmp/foo.img 65536
mount -o loop /tmp/foo.img /mnt
dd if=/etc/motd of=/mnt/test bs=4k >& /dev/null
dd if=/etc/motd of=/mnt/test conv=notrunc seek=32 bs=4k >& /dev/null
dd if=/etc/motd of=/mnt/test2 bs=4k >& /dev/null
dd if=/etc/motd of=/mnt/test2 conv=notrunc seek=1024 bs=4k >& /dev/null
lsattr /mnt/test*
md5sum /mnt/test* > /mnt/MD5SUMS
umount /mnt
e2fsck -fy -E bmap2extent /tmp/foo.img
mount -o loop /tmp/foo.img /mnt
md5sum -c /mnt/MD5SUMS
lsattr /mnt/test*
umount /mnt
----- cut here -----

Maybe you can come up with a simple repro case that fails for you?

Or take an e2image of one of the affected filesystems so that the
developers can directly reproduce your error case. :)

e2image -Q /dev/sda1 /some/qcow/dump/file

(Preferably xz the dumpfile before uploading...)

--D

Thanks,

						- Ted