NX script, still broken

I looked at the thread began by Veli-Matti Lintu entitled "nxagent 
continued.." and tried his script with nx-3.2.0 in Fedora.  It is an 
interesting approach that does indeed work transparently with no other 
LTSP changes.  This approach shims nxagent between the X clients (i.e. 
gnome-session) and the X server with a proxy X server that merely 
reduces the network round-trips.  This approach is interesting but 
ultimately proves to be unusable for a few reasons.

1) NX is a horrible piece of software with a tremendous amount of bugs 
making it barely usable.  Examples: nxagent doesn't work on x86_64 at 
all, had to use i386.  It still has hard coded paths in /usr/X11R6. 
nxagent needs a long delay before it will handle X clients.  The "wait 
for SIGUSR1" thing is unsafe to depend on with nxagent.  There were 
other problems as well...
2) This approach did successfully reduce Youtube video playing from 
65mbit/sec to 20mbit/sec for example.  But it also made it impossible to 
do remote GL like compiz.
3) That Youtube video was reduced in bandwidth substantially by making 
it very jerky and unviewable.  Also interactivity with the X session 
over the network took 20-30 seconds for a click to be recognized while 
it was going on.  Unusable.

I suppose it *could* be more interactive with a full end-to-end NX 
session.  I will attempt to try this later, but I am not holding out hope.

Below is the improved script with notes.

#!/bin/bash

SESS_DISPLAY=1000

# XXX: We would need a better way to do this.
# This is racy and INSECURE.
# It writes to /tmp/.X11-unix/ which any user can write, and it is
# totally predictable because it is incremental.
# Even randomized it is unsafe and should not be shipped in any
# distribution.
while true
do
     let TEST_DISPLAY=$SESS_DISPLAY+6000

     if [ -f /tmp/.X${SESS_DISPLAY}-lock ]; then
         let SESS_DISPLAY=$SESS_DISPLAY+1
         continue
     fi

     if [ -f /tmp/.X11-unix/X${SESS_DISPLAY} ]; then
         let SESS_DISPLAY=$SESS_DISPLAY+1
         continue
     fi

     if nc -z 127.0.0.1 $TEST_DISPLAY 2>/dev/null
     then
         let SESS_DISPLAY=$SESS_DISPLAY+1
         continue
     fi

     break
done

# Identify the specific entry in xauth that we want to copy
case "$DISPLAY" in
     localhost*)
         # ssh forwarded xauth proxy or local X server
         REALDISPNUMBER="${DISPLAY##localhost:}"
         # we need the two spaces after
         XAUTHENTRY="unix:$(echo $REALDISPNUMBER | awk -F'.' '{print 
$1}')  "
         ;;
     *)
         # assume hostname or IP address
         XAUTHENTRY="$DISPLAY"
         ;;
esac

KEY=$(xauth list | grep "$XAUTHENTRY"| awk '{print $3}')
PROTOCOL=$(xauth list | grep "$XAUTHENTRY"| awk '{print $2}')

### It turns out that the way it was grabbing keys from xauth was wrong.
### It was grabbing old stale keys because it was doing it in the same
### fashion as ldm's script, which grabs the wrong key in this case.
### I fixed that above, but then realized that we do not even want this
### key.  We want a new key generated for nxagent... so the above should
### be ripped out.

KEY=`mcookie`
PROTOCOL=MIT-MAGIC-COOKIE-1
xauth remove :${SESS_DISPLAY}
xauth add :${SESS_DISPLAY} ${PROTOCOL} ${KEY}
ulimit -c unlimited
/usr/bin/nxagent :${SESS_DISPLAY} -D \
-auth ~/.Xauthority -nopersistent -noignore &
ulimit -c 0

# UGLY HACK: We need to properly detect that X is done launching before
# proceeding
# Normally you would wait for SIGUSR1 from the child process, but
# we can't do that in a shell script.  Another approach is to run
# an X client in a loop.
if [ -x /usr/bin/setxkbmap ]; then
     while true; do
         #/usr/bin/setxkbmap 2> /dev/null
         /usr/bin/xhost
         RETVAL=$?
         if [ $RETVAL -eq 1 ]; then
             sleep 0.2
         else
             break
         fi
     done
fi

# But that didn't work!  nxagent tells the X client that it is ready,
# but then proceeds to fail when gnome-session talks to nxagent.
# An arbitrary delay before gnome-session seems to solve this issue.

sleep 5
export REAL_DISPLAY=${DISPLAY}
DISPLAY=:${SESS_DISPLAY} /usr/bin/gnome-session

Warren Togami
[email protected]

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