plugin_version

[Ondřej Surý]

I believe that `NS_PLUGIN_VERSION` is reserved for situations
where the **plugin** API itself changes. But I agree with you that
the current situation where the query_ctx_t struct members are
accessed directly isn't ideal.

My recommendation would be to recompile the plugin together
with each new BIND 9 version.

I am open to any suggestions, but I think the having a GitLab
issue would be a better venue to record any ideas around the
plugin system.

Ondrej
--
Ondřej Surý (He/Him)
ondrej at isc.org

My working hours and your working hours may be different. Please do not feel obligated to reply outside your normal working hours.



> On 15. 12. 2022, at 21:47, Marcus Kool <marcus.kool at urlfilterdb.com> wrote:
> 
> Hi Ondrej,
> 
> yeah, I was kinda expecting "no guarantees", but isn't the plugin_version() function a good method candidate to enforce compatibility?
> I mean, isn't increasing NS_PLUGIN_VERSION when a (plugin visible) data structure changes, a good way to enforce that only compatible plugins are used?
> 
> Thanks,
> 
> Marcus
> 
> 
> 
> On 15/12/2022 19:32, Ondřej Surý wrote:
>> Hi Marcus,
>> 
>> I am afraid that we can’t provide any guarantees about the BIND 9 internal libraries. We made a decision to drop the layers and layers of compatibility for the sake of maintainability.
>> 
>> That said, once the release is pronounced ESV (roughly a year from initial release), we try to minimize changes to that branch, but it could still happen if needed by a security fix.
>> 
>> As for the binary compatibility, there’s no guarantee whatsoever, I think you need to match the full version to check whether the plug-in should be loaded.
>> 
>> Honestly, the best way how to keep the plug-in that’s useful for wider audience maintained would be to contribute it to the BIND 9 with a promise that the authors will keep helping maintaining the plug-in. (We would like to avoid the situations where the author just dumps the code on us and don’t care anymore - there’s associated maintenance cost with any new feature.)
>> 
>> Ondrej
>> --
>> Ondřej Surý — ISC (He/Him)
>> 
>> My working hours and your working hours may be different. Please do not feel obligated to reply outside your normal working hours.
>> 
>>> On 15. 12. 2022, at 20:10, Marcus Kool <marcus.kool at urlfilterdb.com> <mailto:marcus.kool at urlfilterdb.com> wrote:
>>> 
>>> 
>>> Hi,
>>> 
>>> I have written a plugin for named and was wondering what the policy behind the usage of plugin_version() is and what kind of compatibility check it intends to perform.
>>> 
>>> It is common for plugins to use query_ctx_t and its members fname, view, client (client.message, client.query) etc.
>>> Since these data structures may change between (patch) versions, a plugin compiled for version A can get a SEGV signal because a data structure changed and the plugin is used inside named version B.
>>> I have little experience with data structure changes of named and observed only the addition of refresh_rrset in query_ctx (somewhere between 9.16.1 and 9.16.35) which did not cause an issue since its 1-byte size did not change offsets of most members inside the query_ctx struct.
>>> 
>>> In our plugin, plugin_register() checks for the major and minor version number in named_g_version so a plugin compiled with 9.16.x refuses to initialize inside a 9.18.y named process and vice versa.  But I have the impression that this might not be a 100% guarantee that all is well.
>>> 
>>> Because we like to release as few as possible versions of the plugin I have a second question: how can we be sure that a plugin compiled with 9.X.1 will have no issues accessing named data structures for all patch versions of 9.X?
>>> 
>>> Thanks,
>>> 
>>> Marcus
>>> 
>>> 
>>> 
>>> 
>>> 
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