Bug#856337: systemd: please support kernel 4.4, or don't hardcode dm interface versions

[Christian Hofstaedtler]

* Michael Biebl <biebl at debian.org> [170228 14:57]:
> TBH, I find it rather broken having to embed a local copy of dm-ioctl.h
> to work around this.

My feeling as well.

> Christian, this version mismatch, does that happen for minor version
> differences as well, like say 4.10.0 vs 4.10.1 or only major versions
> like 4.10.x vs 4.11.x?

The exact code in the kernel is:

|   if ((DM_VERSION_MAJOR != version[0]) ||
|       (DM_VERSION_MINOR < version[1])) {
|       DMWARN("ioctl interface mismatch: "
|              "kernel(%u.%u.%u), user(%u.%u.%u), cmd(%d)",
|              DM_VERSION_MAJOR, DM_VERSION_MINOR,
|              DM_VERSION_PATCHLEVEL,
|              version[0], version[1], version[2], cmd);
|       r = -EINVAL;

So: patchlevel (4.10.0 vs 4.10.1) does not matter, the 'minor'
version (10 in 4.10) of userspace has to be lower or equal to the
kernel's number. 

The bump from 4.34 to 4.35 happened in linux.git
545ed20e6df68a4d2584a29a2a28ee8b2f7e9547 which was then part of
kernel 4.8.

-c