[PATCH xinit 2/2] startx: Make startx auto display select work with per user /tmp dirs

[Peter Hutterer]

On Mon, Mar 23, 2015 at 02:16:13PM +0000, Jon TURNEY wrote:
> 
> 
> On 20/03/2015 17:16, Ray Strode wrote:
> >On Fri, Mar 20, 2015 at 10:02 AM, Hans de Goede <hdegoede at redhat.com> wrote:
> >>If a separate /tmp per user is used the existing auto display select code
> >>does not work, add an extra check for the unix socket for the display number
> >>existing in /proc/net/unix (linux only).
> >
> >This patch and the previous patch make sense to me near term.  It
> >fixes some corner
> >cases without regressing any others.  I do think a better medium-term
> >solution would
> >be for xinit to start using -displayfd and startx to drop its "try to
> >figure out a display
> >number" heuristics.  There's just no reason programs that start an X
> >server should be
> >trawling around in /tmp and/or binding to sockets up front (except for
> >hysterical raisins)
> 
> I wrote a patch [1] a while ago to teach xinit to handle the -displayfd
> option.
> 
> If I understand you correctly, you are suggesting something slightly
> different, that -displayfd should be used by default if a display number
> isn't explicitly specified, but this might serve as a starting point...
> 
> [1] http://cgit.freedesktop.org/~jturney/xinit/commit/?id=c6dc4db8fdcbe115867f6f4a1ab9138536f99fec

The patch itself looks fine, minus a couple of coding style differences with
the rest of the file. they should be fixed. Plus, you're leaving the pipe
open from what I can tell.

What gets interesting is using that from startx. The order of startx is
pretty much:
1) dig around in the system to find a suitable $DISPLAY
2) add xauth entries for $DISPLAY 
3) xinit

Now, I've tried to avoid anything xauth-related, but from the little I know:
to support displayfd in startx you'd have to communicate back to startx
about the $DISPLAY and do the xauth dance before continuing with the xinit
initial client connection. AFAICT, that's the tricky bit about -displayfd
support in startx. Does that make sense or am I way off here?

Cheers,
   Peter