Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!gatech!ncsuvx!mcnc!rti!xyzzy!bert!throopw
From: throopw@bert.dg.com (Wayne A. Throop)
Newsgroups: comp.os.minix
Subject: Re: fork
Message-ID: <3927@xyzzy.UUCP>
Date: 8 Mar 89 20:21:00 GMT
References: <1989Mar3.174924.977@utzoo.uucp> <85830@felix.UUCP>
Sender: usenet@xyzzy.UUCP
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> preston@felix.UUCP (Preston Bannister)
>> henry@utzoo.uucp (Henry Spencer) (paraphrased by Wayne Throop)
>> [... there is many a dup() 'twixt fork() and exec() ...]
> What I _meant_ (as opposed to what I said :-) was that fork() calls are
> almost always followed very closely by exec().  The point I am trying to
> make is that the child-is-copy-of-parent semantic of fork() is irrelevant to
> _most_ programs.  [... and vfork() better represents real needs ...]

Well....  no.  Vfork does nothing that a properly implemented fork can
not do (that is, essentially nothing aside from the copying of the data
that the child actually faults on for writing).   Vfork was a self-admited
kludge introduced because the VM system of some version of the BSD lost
in the mists of time didn't do an adequate job in supporting fork.

On the other hand, I agree that it *might* be a good thing to support
a non-copying-semantic method of process creation.  It's just that the
interaction of vfork() with exit() and exec() is bogus, and a much more
excellent method would be to have push/pop of file descriptor and
signal state operations, along with a create-process operation.  This would
give the advantages of vfork (that is, efficency with inadequate or overly
simple VM implementations) without the appearance of klugery.

On the other hand, we've just added three system calls to handle a case
which is just a subset of the possibilites given by appropriate use of
fork() and exec().  Leave aside the fact that the case covered by the
three additional systems calls is the most common... it's still pretty
clear that fork() + exec() is exactly the right division of responsibility
if what you want is neat, sweet, and petite.

--
Have you heard of the wonderful one-hoss shay,
That was built in such a logical way
It ran a hundred years to a day?
                              --- Oliver Wendell Holmes
--
Wayne Throop      <the-known-world>!mcnc!rti!xyzzy!throopw