lib/libc/x86/sys/__vdso_gettc.c: Conditionalize hyperv support based on MK_HYPERV

[ngie]

Summary

This conditionalizes hyperv support in gettimeofday based on MK_HYPERV, so systems where the administrator has made a conscious decision not to build hyperv support in the system will not be hit by the hyperv path.

MFC after: 3 weeks
Sponsored by: Dell EMC Isilon

[ngie]

Tweak a comment marking the end of the WANT_HYPERV #endif .

[sepherosa_gmail.com]

I don't see why it is needed. If hyperv is not in kernel or the ref rdtsc is not the current timecounter, this path will never be hit. Or do you have other concerns?

[ngie]

In D9242#191080, @sepherosa_gmail.com wrote:

I don't see why it is needed. If hyperv is not in kernel or the ref rdtsc is not the current timecounter, this path will never be hit. Or do you have other concerns?

I just saw that it only hits this case if the time counter is enabled, and after that only hits it if opening the character device succeeds.

It's not an issue today because MK_HYPERV != no doesn't control hyperv header installation, but if that ever changes (and I would kind of like that to be honest), then this would be an issue.

So, the reasoning I claimed here originally might be a bit misleading, but this unfortunately stands in the way of removing the hyperv headers from the system when MK_HYPERV == no.

[sepherosa_gmail.com]

OK, I see. Please fix the commit message when committing then. BTW, in addition to include/dev/hyperv, there are usr.sbin/hyperv and several manpages that you probably want to manage w/ MK_HYPERV.

[sepherosa_gmail.com]

lib/libc/x86/sys/__vdso_gettc.c

220 ↗

(On Diff #24189)

WANT_HYPERV, i.e. no __ prefix.

[ngie]

lib/libc/x86/sys/__vdso_gettc.c

220 ↗

(On Diff #24189)

Thanks :)!