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Date: Mon, 22 Nov 2010 21:01:05 -0500 (EST)
From: Rick Macklem <rmacklem@uoguelph.ca>
To: John Baldwin <jhb@freebsd.org>
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Cc: freebsd-fs@freebsd.org, Ivan Voras <ivoras@freebsd.org>
Subject: Re: preferred kernel upcall method to master nfsd
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> 
> nfsd is a user process. I suspect that when it receives a signal it
> falls out of
> nfssvc() with EINTR and handles saving the restart file in userland.
> Is that close
> to the process Rick or does you need to send a signal between threads
> that are
> exclusively within the kernel?
> 
Yep, the kernel nfsd thread needs to tell the userland master nfsd to
make a backup copy of the stable restart file now.

Doing it with signals, the kernel code would post a signal (SIGUSR2 ?)
to the master nfsd (which is normally in userland).

The master nfsd would simply have a signal handler for SIGUSR2 that would
copy the file (it's pretty small) to a backup copy.

At least that's how I would think I could code it. I haven't actually
tried it?

My question was mostly if there was a preferred/better way for the
kernel code to tell the userland master nfsd to copy the file?

rick