Object structure change

[Andreas Ericsson]

On 02/25/2013 07:11 PM, Ton Voon wrote:
> Hi,
> 
> Looking through recent commits, I came across 2601, which is a port
> of 2600, to fix a downtime issue.
> 
> There is a change to downtime.h to add a new attribute to the
> downtime object.
> 
> Am I right in saying that this is a object structure change and thus
> will affect the binary compatibility of all broker modules? If so,
> this is a problem for Nagios 4 which is in a structure freeze before
> release, but more seriously it is a problem in the Nagios 3.4 branch
> which will silently break lots of broker modules.
> 

It's an ABI incompatibility, so it requires a recompile of affected
modules. No modules use the modified function calls, so for that part
it doesn't matter in practical terms, although it's academically
horribly (which is to say; It only matters if you're interested in
intellectual masturbation). Nagios 3 with the patch should really be
released as 3.5 though. For Nagios 4 it's ok to make this change
(although I'm not very happy about it).

On a side-note, the downtime handling needs to be rewritten more or
less completely. I've started it, but the old code has to remain in
place (as a shim, preferrably) until 5.0 to retain api compatibility.

To clarify, here are the "rules" which we try to adhere to:
API change (requires major release):
 * remove things from structs
 * remove or modify existing functions
 * remove existing types
 * rename existing types without backwards compatibility hacks
  ("#define comment nagios_comment" is the compat hack)

ABI change (requires minor release and module recompilation):
 * add stuff to structs
 * reorder structs

API addendum (requires API minor-version extension marker):
 * add new types
 * add new API's
 * add functions to API's

Shimming (requires nothing at all):
 * Add new API
 * Rewrite old API in ABI-compatible way to front the new API
 * Use new API in core code

Normally, ABI change and API addendum go hand in hand when doing
optimizations, and sometimes when doing bugfixes.

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

Considering the successes of the wars on alcohol, poverty, drugs and
terror, I think we should give some serious thought to declaring war
on peace.

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