Re: when to bump library versions (was: <blank>)

[George Dunlap <George.Dunlap@eu.citrix.com>]

On Thu, May 19, 2016 at 4:01 PM, Jan Beulich <JBeulich@suse.com> wrote:
>>>> On 19.05.16 at 16:53, <roger.pau@citrix.com> wrote:
>> On Thu, May 19, 2016 at 08:44:59AM -0600, Jan Beulich wrote:
>>> >>> On 19.05.16 at 16:34, <roger.pau@citrix.com> wrote:
>>> > We could even have the
>>> > library name versions be set based on XEN_VERSION and XEN_SUBVERSION, so
>>> > that we don't need to go around the different library makefiles bumping the
>>> > versions manually.
>>>
>>> But so far these two are intentionally private to the xen/ subtree.
>>
>> Maybe I'm missing something, but couldn't they be global to the whole tree?
>> (Config.mk seems like a suitable place).
>
> I think originally the idea was that the tool stack isn't really tied to
> a specific hypervisor version. What it is tied to is an interface
> version (of namely domctl and sysctl).

Sure -- but is this actually useful, and even if it is, is it worth the cost?

Advantages of bumping version number only when the interface actually changes:

* Someone who links against an unstable library can in theory re-use
the same binary after upgrading without re-compiling, *if* the
interface didn't change

Advantages of bumping the version number as soon as the tree opens:

* We don't have to think about whether we need to bump the interface
version or not; it happens as part of the branching checklist
* You can install the most recent release and xen on the same box
without the libraries (which may actually be incompatible, since the
interface may have changed without the version number being bumped)
being overwritten.

Looking just at those, I think it's pretty clear which is more useful.
Are there other angles we should consider?

 -George

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