[dm-devel] partx fails 4096 block size

[Bryn M. Reeves]

On Mon, Sep 15, 2014 at 02:48:23PM -0500, Ross Anderson wrote:
> I'd appreciate any help in troubleshooting this. Quiet frustrating not being
> able to use mpath on 4k blocks.

Doesn't seem related to sector size.
 
> http://pastebin.com/EbTMXdvE

> ###partx -a-v
> partition: none, disk: /dev/dm-0, lower: 0, upper: 0
> /dev/dm-0: partition table type 'gpt' detected
> partx: /dev/dm-0: adding partition #1 failed: Invalid argument

partx is trying to call a BLKPG partition management ioctl on a
device-mapper device. Since dm devices are not partitionable it
fails with EINVAL.

> partx: /dev/dm-0: adding partition #2 failed: Invalid argument
> partx: /dev/dm-0: error adding partitions 1-2

The partx program comes from the util-linux package:

$ qwhich partx
util-linux-2.24.2-1.fc20.x86_64

You're probably looking for kpartx which is part of multipath-tools. On
Red Hat distros it's in a separate sub-package named kpartx:

$ qwhich kpartx
kpartx-0.4.9-56.fc20.x86_64

The kpartx command reads partition data from the disk and creates
device-mapper linear maps corresponding to each discovered partition.
This allows you to access the partitions on a device-mapper device as
separate dm devices (e.g. you'd get devices with paths like
'/dev/mapper/dm-0p1' or whatever depending on the -p switch given).

Most distros today will automatically run kpartx when new multipath
devices appear or when they change so you shouldn't need to run it
manually all the time.

Regards,
Bryn.