Hi Eduard, On Sat October 1 2005 6:20 am, Eduard Bloch wrote: > I am trying to create a modified KNOPPIX using devmapper RW snapshots > instead of its unionfs solution. The problem is: I get corrupted data > and cannot see where it comes from. The relevant part of setup code > is attached below. The resulting snapshot volume looks ok at the first > glance (dmsetup status) and can be mounted (ext2), the directory tree is > displayed but it returns corruped data on most files. I cannot see the > problem, a simulation with the same setup method in another environment > (kernel 2.6.13) did work as expected. Also Ubuntu uses that method for > their Live CD and there it works as well. > > I looked for a good and up-to-date documentation of the snapshot target > but could not find anything. I hope someone can give me a clue, I cannot > see how I could solve the problem now. > > # state: KNOPDEV is /dev/cloop, readonly block device and mounted on > # /KNOPPIX, DMSETUP is a static. linked version from devmapper-1.01.04, > # kernel is .2.6.12 (.4 or so) > COW_NAME=COW > CHUNK_SIZE=8 > SNAPSHOT_NAME=knop_rw > VOL_SIZE=$(blockdev --getsize $KNOPDEV) > > # create space for the cow data and assign it to a free loop device COWDEV > echo | dd bs=1 of=/ramdisk/$COW_NAME seek=`expr 512 \* $VOL_SIZE` count=1 \ > 2>/dev/null > for x in /dev/loop* ; do > if losetup $x >/dev/null 2>&1 ; then > continue > else > COWDEV=$x > break > fi > done > losetup $COWDEV /ramdisk/$COW_NAME > > umount /KNOPPIX > # critical part, no /KNOPPIX/* system tools for now > $DMSETUP mknodes > echo "0 $VOL_SIZE linear /dev/cloop 0" | $DMSETUP create knop_ro If /dev/cloop is read-only (and apparently unmounted anyway), you shouldn't need to create the knop_ro device. You can just use /dev/cloop directly. > # this was expected to be a workaround, mapping the loop device to a > # devmapper volume. It did also fail when using pure $COWDEV > echo "0 $VOL_SIZE linear $COWDEV 0" | $DMSETUP create cow This also should not be necessary. What kind of failure do you get if you use $COWDEV directly? > echo "0 $VOL_SIZE snapshot /dev/mapper/knop_ro /dev/mapper/cow p \ > $CHUNK_SIZE" | $DMSETUP create $SNAPSHOT_NAME Based on what I mentioned above, this could be: echo "0 $VOL_SIZE snapshot /dev/cloop $COWDEV p $CHUNK_SIZE" | \ $DMSETUP create $SNAPSHOT_NAME > $DMSETUP mknodes $SNAPSHOT_NAME > > #remount > /static/mount /dev/mapper/$SNAPSHOT_NAME /KNOPPIX > # we are back, rewritable > bash > # And this bash command running on /KNOPPIX already fails with obscure > # errors. I just ran a similar test (on a 2.6.12 kernel): # Create loop devices dd if=/dev/zero of=loop_file0 bs=1M count=1 seek=1024 dd if=/dev/zero of=loop_file1 bs=1M count=1 seek=1024 losetup /dev/loop0 loop_file0 losetup /dev/loop1 loop_file1 # Create filesystem on first loop device and copy some data to it. mkfs.ext3 /dev/loop0 mount /dev/loop0 /mnt/loop0/ cp -a /usr/src/linux-2.6.12 /mnt/loop0/ umount /mnt/loop0 # Create the snapshot. echo "0 `blockdev --getsize /dev/loop0` snapshot /dev/loop0 /dev/loop1 p 8" \ | dmsetup create loop_snap # Mount the snapshot. Compare data and modify data. mount /dev/mapper/loop_snap /mnt/loop_snap cd /mnt/loop_snap diff -Naur --brief linux-2.6.12 /usr/src/linux-2.6.12 cp -a /usr/src/linux-2.6.11 . rm -rf linux-2.6.12 diff -Naur --brief linux-2.6.11 /usr/src/linux-2.6.11 cd / # Unmount the snapshot. Deactivate and reactivate the snapshot. Mount again # and compare and modify data again. umount /mnt/loop_snap dmsetup remove loop_snap echo "0 `blockdev --getsize /dev/loop0` snapshot /dev/loop0 /dev/loop1 p 8" \ | dmsetup create loop_snap mount /dev/mapper/loop_snap /mnt/loop_snap cd /mnt/loop_snap diff -Naur --brief linux-2.6.11 /usr/src/linux-2.6.11 rm -rf linux-2.6.11 I have not seen any kind of errors at all. What specific errors are you getting? Anything in the kernel log? Can you test again without the extra dm-linear devices? -- Kevin Corry kevcorry@xxxxxxxxxx http://www.ibm.com/linux/ http://evms.sourceforge.net/ -- dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
