Re: bug#54245: 29.0.50; select usage in GNUstep

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: Robert Pluim <rpluim@gmail.com>,  larsi@gnus.org,  emacs-devel@gnu.org
> Date: Mon, 14 Mar 2022 21:34:02 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > The HAVE_SELECT in msdos.c is for the (old and quite defunct) MSDOS
> > build with Xlib (yes, there was such a beast: see those HAVE_X_WINDOWS
> > in msdos.c?), so IMNSHO we can simply drop HAVE_SELECT in msdos.c.
> 
> When I had the time a few weeks ago, I looked into resurrecting the X11
> build on MS-DOS, but could not find any information about an Xlib
> implementation for DJGPP.  So I can't help but wonder exactly what
> enviroment that build once ran on.
> 
> I'd be indebted to anyone with that information.

The environment was DesqView/X.  It came with a tailored version of
Xlib and other X libraries/utilities that ran on plain MS-DOS using (I
think) the DesqView's own QEMM DOS extender.  This was before DJGPP
v2.x was developed that uses DPMI to switch the processor into
protected mode and run 32-bit protected-mode code that uses virtual
memory.

That's all I know.  I never myself built such an Emacs, and never used
DesqView/X.  See https://en.wikipedia.org/wiki/DESQview for more.

Note that nowadays you'd need such an Xlib compiled with DJGPP v2.x,
which could run in the DPMI environment, so if DesqView/X is still
available somewhere, you will probably need to use QDPMI on plain
MS-DOS.  And if you run on plain MS-DOS, you'd have gazillion problems
with long file names that clash in the 8+3 namespace, because Emacs
stopped trying to be 8+3 clean long ago.

So resurrecting such a build would be a non-trivial project.