Re: [PATCH 1/2] Revert "xfrm: interface with if_id 0 should return error"

["Kai Lüke" <kailueke@linux.microsoft.com>]

Hi,
> Whereas 8dce43919566 ("xfrm: interface with if_id 0 should return error")
> involves xfrm interfaces which don't appear in the pull request.
>
> In which case, why should that commit be reverted?

Correct me if I misunderstood this but reading the commit message it is
explicitly labeled as a behavior change for userspace:

    With this commit:
     ip link add ipsec0  type xfrm dev lo  if_id 0
     Error: if_id must be non zero.

Changing behavior this way is from my understanding a regression because
it breaks programs that happened to work before, even if they worked
incorrect (cf. https://lwn.net/Articles/726021/ "The current process for
Linux development says that kernel patches cannot break programs that
rely on the ABI. That means a program that runs on the 4.0 kernel should
be able to run on the 5.0 kernel, Levin said.").

Regards,
Kai