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Date: Sat, 29 May 2004 12:44:13 +0200
From: "Eli Zaretskii" <eliz AT gnu DOT org>
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To: djgpp AT delorie DOT com
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	(048321887-0001 AT t-online DOT de)
Subject: Re: Using DR-DOS fork in DJGPP
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> From: 048321887-0001 AT t-online DOT de (Udo Kuhnt)
> Newsgroups: comp.os.msdos.djgpp
> Date: 27 May 2004 00:43:26 -0700
> > 
> > Copying the VM is not sufficient: the OS also has to know which file
> > handles the parent process has open, and set up the child process so
> > that it has the same open file handles. 
> 
> This is exactly what "copying the VM" means - all data structures of the old
> VM are being copied into the the new one, including the file data structures.
> So the handles of the child are an exact copy of the parent's ones.

I already explained in another message in this thread that a copy is
not what we want, if we want to emulate the Posix semantics of `fork'.
File handle inheritance is not a simple copy.

Btw, the documentation of Z_DomFork (which is what we are discussing,
I presume) does not say that it simply copies the current VM, it says:

  Z_DomFork creates an exact copy of the current domain, then creates
  a process in it and starts the process executing. The process is
  specified in the PCREATE_PBLK which is identical to that used in the
  X_PCreate call [...]

So after the VM is copied, a new process is started in it.  Whether
this is the same process as the one that called Z_DomFork, and if so,
whether it begins from the same point where we called Z_DomFork, is
left unspecified.

So the question which started this thread, namely: how we can write
an emulation of the Posix `fork' using this API, still stands.

> > Similarly with any other OS resources the child is to "inherit".
> 
> What other resources are you referring to?

Signal handlers, for one.