Re: losetup -d does not move partition devices

[butter@breezl.com]

Hi Karel

Thanks for your detailed explanation. Good to hear I did hit a real
(although already known) issue. Too bad there is no easy fix.

Anyway, one last minor comment: 

Ubuntu 13.04 64bit does not yet support option -P for losetup. So
this must be an older version of util-linux. But then: how do I
determine the version of util-linux installed? The binaries have
no --version option and 'strings /sbin/losetup | egrep '[0-9]' does
not reveal anything useful either. Maybe there is a general version
for util-linux available in another binary? The man page does not
tell. I failed to identify the version number!

Regards
BB.

On 07.10.2013 13:38, Karel Zak wrote:
> On Tue, Sep 24, 2013 at 06:22:11PM +0200, butter@breezl.com 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
>