Re: [meta-oe][PATCH 4/5] gpsd: add optional support for KPPS interface

["Peter A. Bigot" <pab@pabigot.com>]

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@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