On Tue, Sep 24, 2013 at 06:22:11PM +0200, butter@xxxxxxxxxx wrote:
> get deleted when you call "losetup -d DEVICE". This causes other programs
> (like lvmdiskscan -l) to report Input/output errors.
>
> Here is how to reproduce the problem:
>
> LOOPDEV=/dev/loop3
> IMAGEFILE=`pwd`/mydisk.img
> MOUNTPOINT=`pwd`/mnt
>
> # 1. Create and mount an ext4 partition from a file-based disk image
> dd if=/dev/zero of=$IMAGEFILE bs=1M count=80
> sudo losetup $LOOPDEV $IMAGEFILE
kernel uses partitions on loop devices conditionally, and here you said
"I don't care about partitions...". You have to use
sudo losetup -P $LOOPDEV $IMAGEFILE
if you want to force kernel loopdev driver to use partitions.
> sudo parted $LOOPDEV mklabel msdos
> sudo parted $LOOPDEV mkpart primary 2048s 43007s
> sudo mkfs -t ext4 ${LOOPDEV}p1
> mkdir $MOUNTPOINT
> sudo mount ${LOOPDEV}p1 $MOUNTPOINT
>
> # 2. Unmount again => ERROR: the partition device files are not deleted
> sudo umount $MOUNTPOINT
mount/umount is completely irrelevant for this issue. The simple way
to reproduce the problem is:
dd if=/dev/zero of=img bs=1M count=80
losetup -f img --show
parted /dev/loop0 mklabel msdos
parted /dev/loop0 mklabel msdos
losetup -d /dev/loop0
cat /sys/block/loop0/size
cat /sys/block/loop0/loop0p1/size
Anyway, the problem is that parted uses BLKPG_ADD_PARTITION ioctl to create
/dev/loop0p1, but the loop0 device has been created without PARTSCAN flag
(see /sys/block/loop0/loop/partscan). It means that loopdev kernel driver
does not call BLKRRPART during loop0 cleanup (loop_clr_fd() in kernel code).
You can remove the partition manually by BLKPG_DEL_PARTITION ioctl:
# partx -d /dev/loop0p1
... but this all is known issue, Phillip Susi tried to fix this
disadvantage, but his solution has been reverted (see kernel commit
c2fccc1c9f7c81700cbac2120a4ad5441dd37004).
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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