Re: [RFC PATCH] genetlink: add multi-version family support for protocol negotiation

[Christoph Böhmwalder]

Am 16.03.26 um 19:37 schrieb Jakub Kicinski:
> What's the delta between the families? Do you have any examples of 
> the the version ends up being used?

The main difference between DRBD 8 and 9 in general is that 8 only
replicates to a single peer, while 9 has support for multiple peers.
This also introduces major changes in the genl family. For example, the
"connect" command works completely differently between the v1 and v2
families.
In v1, it takes all the net_conf parameters and immediately sets up the
connection.
In v2, you need a new_peer / new_path command first; the net_conf is
passed to new_peer in this case. The connect command then only
"activates" the connection.
So the semantics are completely different.

Other commands (like "state_info") were removed entirely and split up
into different commands.

The specific exact diff is available as part of our prototype DRBD 9
branch (included in linux-next):
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/diff/include/linux/drbd_genl.h?id=11b8887a3efae2868037f2bd8dbbc68a8591f66c

As for the usage: the plan is for drbd to register its family with
min_version=1, max_version=2. Then we would dispatch the v2 commands
normally, and the v1 commands through a thin compat layer.
In the in-tree DRBD, the version is currently unused. In the (still
out-of-tree) DRBD 9 though, we do check that the version is what we expect:
https://github.com/LINBIT/drbd/blob/master/drbd/drbd_nl.c#L426

This would be replaced by the mentioned compat dispatch logic once we
have in-kernel infrastructure for supporting multiple versions.

Best Regards,
Christoph

-- 
Christoph Böhmwalder
LINBIT | Keeping the Digital World Running
DRBD HA —  Disaster Recovery — Software defined Storage