svn commit: r190865 - in head: sbin/ipfw sys/netinet

[Luigi Rizzo]

On Thu, Apr 09, 2009 at 02:25:59PM +0100, Robert Watson wrote:
> On Thu, 9 Apr 2009, Luigi Rizzo wrote:
> 
> > Note- this commit changes the userland/kernel ABI for pipes
> > (but not for ordinary firewall rules) so you need to rebuild
> > kernel and /sbin/ipfw to use dummynet features.
> >
> > Please check the manpage for details on the new feature.
> >
> > The MFC would be trivial but it breaks the ABI, so it will
> > be postponed until after 7.2 is released.
> 
> Under our more strict but relatively undocumented -STABLE ABI rules, this 
> sort of change is no longer permitted.  Is there really no way to do this 
> without breaking the ABI for the purposes of making it more gently MFCable?

There is always a way, and it is to provide, within the kernel,
some translation glue so that requests issued in "ancient greek"
(i.e. the old ABI) will still be accepted and answered properly.
while at the same time provide a new ABI that supports the
new functionalities.

This is what will be done eventually.  For now, it is not my intention
to do the MFC of _this_ version of the code, it was more a comment
for people who asked me this feature on RELENG_7.

Unfortunately the "struct dn_pipe" and "struct dn_flow_queue" are
not particularly well designed for extensibility (my fault, but it
was 10 years ago).

Also note that the version in RELENG_7 will definitely need an
update because some numeric fields are 32-bit and in this age of
Gbit/s links and GHz CPUs are in constant danger of overflow (with
the code going to great lengths to minimize the problems).

The planned course of action before the MFC is:

+ add a version/len field to the structure(s) to improve
  ABI compatibility, as it was done in 2002 for ipfw;
+ separate the kernel-only information from the one visible
  to userland, so the ABI problems will be less likely to appear
  again;

Once this is done and stabilized, I will try to do an MFC that,
among other things, will use a new sockopt for the new ABI, and
include the translation glue for the old ABI.

cheers
luigi