cvs commit: src/lib/libc/locale utf8.c

[John Baldwin]

On Thursday 25 October 2007 07:04:08 pm Scott Long wrote:
> Robert Watson wrote:
> > On Thu, 25 Oct 2007, Andrey Chernov wrote:
> > 
> >> On Thu, Oct 25, 2007 at 12:05:40PM -0700, LI Xin wrote:
> >>> Well, I think the problem is not exposing a new symbol by itself, but 
> >>> __mb_sb_limit is being used in _ctype.h, in a form of __inline 
> >>> functions. Therefore, the change will break new binaries running on 
> >>> older systems.
> >>
> >> Yes. Only vice versa compatibility supported.
> > 
> > I think the issue here is that the change occurred very quickly after 
> > the branch, and when users wanted to 'change gears' back to RELENG_7 
> > from HEAD once it was created immediately ran into the problem.  It 
> > seems like a useful piece of post-branch advice to developers in the 
> > future will be, "Please don't do things that make switching branches -- 
> > back or forward -- for the first few weeks after the branch is 
> > created".  In general, I don't think we care about forward 
> > compatibility, but we are currently getting lots of reports because this 
> > is one of those few times where a lot of moving backward happens.
> > 
> 
> We do care about forward compatibility within STABLE branches, as Ken
> and I have discussed in side threads.  But yes, forward compat between
> major branches is merely desired; i.e. changes will happen, and
> hopefully not for gratuitous reasons.

If we care about forward compatiblity then we can't add new features to 
RELENG_X branches.  For example, MFCing MSI to 6.x broke forward compat since 
a 6.3 module might call the MSI methods thus can't be used on a 6.2 kernel.  
AFAIK, we have _never_ promised anything wrt forward compat, only backwards 
ABI compat.  I can agree with Robert above that during a transition time such 
as now it's really handy to be able to switch easily between branches, but I 
didn't think it was ever a concern otherwise.  If we are going to change the 
policy for that then there's a whole bunch of crap I need to go back out of 
6.x to restore compat. :-/

-- 
John Baldwin