Don't stat nsswitch.conf all the time.

[trasz]

Summary

Don't call stat(2) on nsswitch.conf(5) every time nsdispatch(3)
and dependent functions (eg getpwname(3)) get called. This can
improve performance of bbinaries that perform a lot of name
lookups, such as gssd(8). It also matches documented behaviour
of Linux and Solaris.

The old code is left in place, should anyone need it, guarded
by #ifdef NS_REREAD_CONF.

Relnotes: yes

[bcr]

OK from manpages. Thanks for the work!

[des]

I would have rejected this change if I had noticed it in time. It is a huge POLA violation, especially on laptops that aren't running their own resolver. There's an intermediate solution, which is to stat the file every M requests and / or N seconds. The caveat is that the latter is very fast on i386, amd64, arm, and arm64, which us a vDSO, but slow on other platforms.

[trasz]

How does it affect laptops without their own resolver? My assumption was the nsswitch.conf is pretty much only ever changed once, during system setup.

[des]

Never mind, I was thinking of resolv.conf...