Re: In-kernel process exit hooks?

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Fri, 8 Jan 2016 11:22:28 +0800 (PHT)
    From:        Paul Goyette <paul%vps1.whooppee.com@localhost>
    Message-ID:  <Pine.NEB.4.64.1601081115270.22533%vps1.whooppee.com@localhost>

  | Is there a "supported" interface for detaching the file (or descriptor) 
  | from the process without closing it?

Inside the kernel you want to follow the exact same procedure as would
be done by

		newfd = dup(oldfd);
		close(oldfd);

except instead of dup (and assigning to a newfd in the process) we
take the file reference and stick it in filemon.   There's nothing
magic about this step.  What magic there is (though barely worthy of
the title) would be in ensuring that filemon properly releases the file
when it is closing.

  | I expect that make(1) assumes the log-fd is still available, and just 
  | follows the example code in filemon(4) man page: when finished logging, 
  | reset the file-pointer to 0 and start reading the data.

make(1) can be changed...   After all, it was added originally, and that
took code changes to make happen.   Further, make must work OK without it,
none of my kernels have filemon included (and they don't load modules),
and make works just fine.

  | Yeah, I was trying to avoid the change in semantics.  :)

Generally a good thing, and if there's a clean way to make it happen,
worth doing.   But this one is a case where that almost certainly doesn't
really matter.

kre