nsswitch.conf: Avoid modification after installation

[markj]

Summary

To implement WITHOUT_NIS, we have a hack in the build which modifies the
installed nsswitch.conf to remove NIS compat providers and databases.
This hack operates on the installed nsswitch.conf, which means that the
installed file size won't match that listed in the metalog.

One option would be to maintain two copies of nsswitch.conf, one for
each configuration, but that would result in duplication and I don't see
a clear way around that.

Instead, stage a copy of nsswitch.conf in the libc objdir, and modify
that one before installing, so that the version recorded in the metalog
matches what actually gets installed.

PR: 209718
Sponsored by: Klara, Inc.
Sponsored by: The FreeBSD Foundation

[kevans]

lib/libc/net/Makefile.inc

182

I somewhat wonder if this should actually be .PHONY -- we don't have a good way to record dependencies on build options, so toggling between WITH and WITHOUT won't regenerate this without manual intervention, presumably

[kevans]

lib/libc/net/Makefile.inc

182

(Realizing that this is a more general problem, but for this speciifc case it could be considered a regression since it previously only mattered the value of the knob at install time)

[emaste]

I think this is a fine short term approach (IMO it's no worse than the existing modify-nsswitch-conf target).

That said maybe we can accommodate @kevans comment with something like

.if ${MK_NIS} != "no"
CONFS+=net/nsswitch.conf
.else
${.OBJDIR}/nsswitch.conf

all: ${.OBJDIR}/nsswitch.conf
...

i.e., if NIS is not turned off we add the unmodified conf file, and if it is turned off we use the extra build stuff?

[markj]

Try to avoid breaking incremental rebuilds if WITHOUT_NIS flips in between
successive builds.

[markj]

lib/libc/net/Makefile.inc

182

I took Ed's suggestion since it lets us avoid doing unnecessary work during incremental builds, which seems like good practice even though it's quite negligible in this case.

[kevans]

lib/libc/net/Makefile.inc

182

Yeah, I quite like that as well - thanks!

[emaste]

This could be done with sed < ${LIBC_SRCTOP}/net/nsswitch.conf > ${.TARGET} rather than the in-place sed, but not a big deal