mustang_bridge_start

#!/usr/bin/python

import os
import sys
from os.path import expanduser
from pwd import getpwnam
from grp import getgrnam

import glob
import syslog
from string import split

import usb.core

rundir = "/var/run/mustang/"

# Mustang USB parms
mustang_vid = 0x1ed8
mustang_pids = ( 0x0004, 0x0005, 0x000a, 0x0010, 0x0012, 0x0014, 0x0016 )

####### Start User Edits #########

# Controller USB parms
control_vid = 0x0763
control_pid = 0x0160

# Controller MIDI device
midi_device = 1

# MIDI listen channel
midi_channel = 1

######## End User Edits ##########

# Look for devices
controller = usb.core.find( idVendor = control_vid, idProduct = control_pid )
if ( not controller ):
    sys.exit( 0 )

mustang = False
for pid in mustang_pids:
    device = usb.core.find( idVendor = mustang_vid, idProduct = pid )
    if ( device ):
        mustang = True
        break

if ( not mustang ):
    sys.exit( 0 )

pid = os.getpid()
# syslog.syslog( "%d: Starting" % pid )

# Look for atomic pid file
os.chdir( rundir )
filelist = glob.glob( 'mustang_*' )
if len( filelist ) != 1:
    syslog.syslog( "%d: /var/run/mustang is not properly setup" % pid )
    sys.exit( 0 )

# Found file.  Parse out the PID of the process that created it.
lockfile = filelist[0]
oldpid = split( lockfile, '_' )[1]

# syslog.syslog( "%d: Check for path /proc/%s" % (pid, oldpid) )
if not os.path.exists( "/proc/%s" % oldpid ):
    # No such process, ok to start ours
    # syslog.syslog( "%d: Renaming %s to mustang_%d" % (pid, lockfile, pid) )
    try:
        os.rename( lockfile, "mustang_%d" % os.getpid() ) 
    except Exception, e:
        pass
        # syslog.syslog( "%d: Unable to rename file" % pid )
    else:
        # syslog.syslog( "%d: About to exec" % pid )
        # Drop privileges and start the program
        pwObj = getpwnam('mustang-user')
        os.setgid( pwObj.pw_gid )
        
        # Need secondary groups to access MIDI and USB devices
        sec_gids = ( getgrnam('plugdev').gr_gid, getgrnam('audio').gr_gid )
        os.setgroups( sec_gids )
        
        os.setuid( pwObj.pw_uid )
        os.execl( "/usr/local/bin/mustang_midi", "mustang_midi", "%s" % midi_device, "%s" % midi_channel )