[oe] [meta-oe][PATCH 4/5] gpsd: add optional support for KPPS interface
Peter A. Bigot
pab at pabigot.com
Thu Aug 28 15:23:54 UTC 2014
On 08/28/2014 09:32 AM, Martin Jansa wrote:
> On Thu, Aug 28, 2014 at 08:05:54AM -0500, Peter A. Bigot wrote:
>> On 08/28/2014 07:53 AM, Burton, Ross wrote:
>>> On 28 August 2014 13:06, Peter A. Bigot <pab at pabigot.com> wrote:
>>>> +PACKAGECONFIG ??= ""
>>>> +PACKAGECONFIG[kpps] = ",,pps-tools"
>>> That's not actually deterministic - if pps-tools is installed but the
>>> packageconfig option is disabled then gpsd will still enable the
>>> support.
>> Yeah, I'm aware of that. It's also not something that can be
>> controlled, since gpsd's author doesn't believe in configuration options
>> to enable features: every capability is enabled or disabled by
>> inspecting the environment at compile-time.
>>
>> Although ntp does support some explicit enable/disable flags, it too
>> fails to provide a way to say "Pay no attention to that PPS header, it
>> isn't really there."
> Then we need to patch their configure.
>
>> For this situation I don't think there's a big issue. The PACKAGECONFIG
>> setting ensures that the header will be available if the feature is
>> desired. If it happens to be present but PPS support isn't explicitly
>> requested, there's no failure in either build or runtime: it's still
>> gated by runtime checks for PPS sources and the option being enabled in
>> the Linux kernel. (There are no runtime libraries that need to be
>> installed to use KPPS.)
>>
>> Is this going to be a problem with the patch being accepted?
> Yes
>
> people can be used to have KPPS support enabled by "accident" e.g.
> because they are building ntp with KPPS support and pps-tools is almost
> always built before gpsd..and then once it's built in different order and end-user will be
> surprised by lost KPPS support from gpsd.
The number of people who will use KPPS is incredibly small, and nobody's
going to use it unintentionally as it requires on-target configuration.
Those who need it, though, have no recourse other than to build ntpd or
gpsd outside of OE if patches like these aren't present.
I understand the reasoning and agree in theory that absolute determinism
would be ideal, but believe hacking the ntp and gpsd configuration
infrastructure to explicitly disable use of a detected PPS header would
present a bigger risk and long-term cost to stability and
maintainability in OE than the possibility you've identified. So that
solution isn't something I'm going to take on.
An alternative is to add kpps to the default PACKAGECONFIG, so the
required header is normally available. The cost of the feature's
presence in the packages is nearly zero (a slight increase in daemon
code size, and an extra check when the process starts.) Would that be
acceptable?
If we can't come to an agreement, then the only patch that's really
important is the first one which restores the ability to diagnose
misconfigured NTP systems. Please let me know whether I should mark the
others as withdrawn in patchwork.
Peter
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