[CentOS] Emulate RHEV On CentOS - A note on Xen v. KVM

[Always Learning]

On Thu, 2011-09-08 at 20:00 -0400, Ross Walker wrote:
> On Sep 7, 2011, at 9:57 AM, Always Learning <centos at u61.u22.net> wrote:
> 
> > Perhaps a silly question, but why maintain patches ? Why not compile a
> > new version and discard all the patches ? Patches are a messy manner to
> > maintain programmes.

> RHEL needs to keep the same ABI (application binary interface) for both
> kernel and user programs so third party VARs and software developer's
> binary packages will continue to be compatible during the lifetime of
> a release (5.X or 6.X).

According to my brief 30 seconds understanding of ABIs from Wikipedia,
that does not seem relevant to patching. The ABI is just a calling
convention. The parameters used and the data exchanged is predetermined
otherwise nothing would work. Parameters and data formats remains
constant throughout the life-time of the software. That has always been
the way for all inter-programme communications.

> In order to do that RH keeps (or makes all attempts to) the same
> versions of the software during the release while back porting
> security updates and must-have features that don't change these ABIs.

Anything which is patched is, by definition, not the same version as the
original version although the version number can remain the same and the
functionality generally remains the same. Obviously the ABI should
remain the same otherwise other programmes would be unable to
successfully exchange 'data'. 

> These back ported updates are the patches that are applied to the base
> package.

Which means some systems, patched locally, may have to then re-apply
their patches to the base system ?

> That should make it crystal clear.

Regrettably it did not. Another poster, whose name I can't recall at
this moment, explained the patched practise as being able to restrict
charges to specific modules while maintaining unaltered core
functionality and having the flexibility to customise a base package for
specific requirements.

Best regards,

Paul.