[dm-devel] dm: introduce DM_GET_TARGET_VERSION

[Mike Snitzer]

On Tue, Sep 17 2019 at 11:44am -0400,
John Dorminy <jdorminy at redhat.com> wrote:

>    Makes sense, sorry I missed that detail.
> 
>    Might it be better to just extend 'dmsetup targets' to take an optional
>    target-name parameter? When I saw this change, I thought 'dmsetup targets
>    <name>' surely worked already for the purpose, and was somewhat surprised
>    when experiment disagreed. Then list_versions() has much the same code
>    change as in this change, there's a little change in validate_params(),
>    and it seems less surprising (to me) to extend the existing
>    target-information-printing dmsetup command than to add another one.

No, I don't think it better to extend 'dmsetup targets'.  There is
little to be gained in doing so.

The DM_GET_TARGET_VERSION ioctl's implementation happens to be shared
with the DM_LIST_VERSIONS ioctl (used by 'dmsetup targets') but that
doesn't imply DM_LIST_VERSIONS should be extended instead.

This is a simple change that enables userspace to accomplish a specific
goal without altering an established DM ioctl.