[dm-devel] dm: introduce DM_GET_TARGET_VERSION

[Mike Snitzer]

On Tue, Sep 17 2019 at  9:56am -0400,
John Dorminy <jdorminy at redhat.com> wrote:

>    I'm confused here:

>    >...and then it fails on activation because DM table load detects old (or
>    missing) dm-crypt feature.
>    >(There was no way to get dm target version before table load if module is
>    not loaded.)
>    >And I tried to avoid modprobe calls from libcryptsetup.
> 
>    I'm not understanding how this could work. Let's say there's a module
>    providing target 'splice' which is currently unloaded. Then `dmsetup
>    target-version splice` is unaware of the splice target, and thus reports
>    nothing. So in order to get the proper version number, we do have to do a
>    modprobe first.
>    But, if the module providing splice *is* already loaded, `dmsetup targets`
>    will report splice's version number already, so `dmsetup target-version
>    splice` is a convenience instead of parsing `dmsetup targets` output?

dm_get_target_type() loads the requested module.  No userspace modprobe
needed.