"Después del juego es antes del juego"
Sepp Herberger

martes, 8 de julio de 2014

Impresoras duplicadas en CUPS

Un problema bastante desconcertante que me ocurría a veces es que las impresoras conectadas por USB me aparecían dos veces en la lista de impresoras y en /etc/cups/printers.conf, como si CUPS  pensase que eran impresoras distintas, aun cuando su DeviceURI era igual. Este problema se hacía mas frecuente cuando cambiaba el nombre de la impresora y ponía uno a mi gusto, en lugar de el que le había dado CUPS en la autodetección, o cuando usaba el filtro tea4cups para controlar los trabajos enviados a las cola de impresión. 

Como utilizo tea4cups para llevar una contabilidad de las páginas impresas, el que las impresoras apareciesen duplicadas me originaba un problema a la hora de recopilar los datos, además de desconcertar al usuario a la hora de imprimir.

Mi compañero Ubaldo me puso en la pista de como resolver el problema. En el paquete system-config-printer-udev están los scripts encargados de manejar las impresoras USB detectadas por udev. En concreto el script /lib/udev/udev-add-printer es el que se encarga de añadir a CUPS una nueva impresora cuando es detectada por primera vez. Estaba claro que algo fallaba ahí y que había que retocar el código del script para evitar que se duplicase. Afortunadamente el script estaba en python.

El script retocado queda así (pongo en rojo las líneas añadidas por mí):

 #!/usr/bin/python  
 ## udev-add-printer  
 ## Copyright (C) 2009, 2010 Red Hat, Inc.  
 ## Author: Tim Waugh <twaugh@redhat.com>  
 ## This program is free software; you can redistribute it and/or modify  
 ## it under the terms of the GNU General Public License as published by  
 ## the Free Software Foundation; either version 2 of the License, or  
 ## (at your option) any later version.  
 ## This program is distributed in the hope that it will be useful,  
 ## but WITHOUT ANY WARRANTY; without even the implied warranty of  
 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the  
 ## GNU General Public License for more details.  
 ## You should have received a copy of the GNU General Public License  
 ## along with this program; if not, write to the Free Software  
 ## Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  
 import cups  
 import cupshelpers  
 import dbus  
 import os  
 import sys  
 import traceback  
 from syslog import *  
 MFG_BLACKLIST=[  
   "graphtec",  
   ]  
 def create_queue (c, printers, name, device_uri, ppdname, info, installer):  
   # Make sure the name is unique.  
   namel = unicode (name.lower ())  
   unique = False  
   suffix = 1  
   while not unique:  
     unique = True  
     for printer in printers.values ():  
       if (not printer.discovered and  
         ((suffix == 1 and printer.name.lower () == namel) or  
          (suffix > 1 and  
          printer.name.lower () == namel + "-" + str (suffix)))):  
         unique = False  
         break  
     if not unique:  
       suffix += 1  
       if suffix == 100:  
         break  
   if suffix > 1:  
     name += "-" + str (suffix)  
   c.addPrinter (name,  
          device=device_uri,  
          ppdname=ppdname,  
          info=info,  
          location=os.uname ()[1])  
   if not installer:  
     # There is no session applet running to deal with installing  
     # drivers so there is a good chance that this queue won't work  
     # right now. If that's the case, delete it. The user can  
     # reconnect the printer when they log in, and everything will  
     # be set up correctly for them at that point.  
     try:  
       ppdfile = c.getPPD (name)  
       ppd = cups.PPD (ppdfile)  
       os.unlink (ppdfile)  
       (pkgs, exes) = cupshelpers.missingPackagesAndExecutables (ppd)  
       if pkgs or exes:  
         # There are filters missing. Delete the queue.  
         syslog (LOG_ERROR, "PPD %s requires %s" % (ppdname,  
                               repr ((pkgs, exes))))  
         syslog (LOG_ERROR, "Deleting non-functional queue")  
         c.deletePrinter (name)  
         name = None  
     except cups.IPPError, (e, m):  
       pass  
     except RuntimeError:  
       pass  
   if name:  
     cupshelpers.activateNewPrinter (c, name)  
   return name  
 def add_queue (device_id, device_uris, fax_basename=False):  
   """  
   Create a CUPS queue.  
   device_id: the IEEE 1284 Device ID of the device to add a queue for.  
   device_uris: device URIs, best first, for this device  
   fax_basename: False if this is not a fax queue, else name prefix  
   """  
   id_dict = cupshelpers.parseDeviceID (device_id)  
   if id_dict["MFG"].lower () in MFG_BLACKLIST:  
     syslog (LOG_DEBUG, "Ignoring blacklisted manufacturer %s", id_dict["MFG"])  
     return  
   syslog (LOG_DEBUG, "add_queue: URIs=%s" % device_uris)  
   installer = None  
   if fax_basename != False:  
     notification = None  
   else:  
     try:  
       bus = dbus.SystemBus ()  
       obj = bus.get_object ("com.redhat.NewPrinterNotification",  
                  "/com/redhat/NewPrinterNotification")  
       notification = dbus.Interface (obj,  
                       "com.redhat.NewPrinterNotification")  
       notification.GetReady ()  
     except dbus.DBusException, e:  
       syslog (LOG_DEBUG, "D-Bus method call failed: %s" % e)  
       notification = None  
     try:  
       obj = bus.get_object ("com.redhat.PrinterDriversInstaller",  
                  "/com/redhat/PrinterDriversInstaller")  
       installer = dbus.Interface (obj,  
                     "com.redhat.PrinterDriversInstaller")  
     except dbus.DBusException, e:  
       syslog (LOG_DEBUG, "Failed to get D-Bus object for "  
           "PrinterDriversInstaller: %s" % e)  
   id_dict = cupshelpers.parseDeviceID (device_id)  
   if installer:  
     cmd = id_dict["CMD"]  
     if cmd:  
       cmd = reduce (lambda x, y: x + ',' + y, cmd)  
     else:  
       cmd = ""  
     try:  
       installer.InstallDrivers (id_dict["MFG"], id_dict["MDL"], cmd,  
                    timeout=3600)  
     except dbus.DBusException, e:  
       syslog (LOG_DEBUG, "Failed to install drivers: %s" % repr (e))  
   c = cups.Connection ()  
   ppds = cupshelpers.ppds.PPDs (c.getPPDs ())  
   (status, ppdname) = ppds.getPPDNameFromDeviceID (id_dict["MFG"],  
                            id_dict["MDL"],  
                            id_dict["DES"],  
                            id_dict["CMD"],  
                            device_uris[0])  
   syslog (LOG_DEBUG, "PPD: %s; Status: %d" % (ppdname, status))  
   if status == 0:  
     # Think of a name for it.  
     name = id_dict["MDL"]  
     name = name.replace (" ", "-")  
     name = name.replace ("/", "-")  
     name = name.replace ("#", "-")  
     if fax_basename != False:  
       name = fax_basename + "-" + name  
     printers = cupshelpers.getPrinters (c)  
     #Comprobamos si ya existe un dispositivo con esa URI igual  
     #o precedida por tea4cups  
     uri=device_uris[0].lower()  
     ya_existe=False  
     for printer in printers.values ():  
       device_uri=printer.device_uri.lower()  
       if device_uri == "tea4cups://" + uri or device_uri == uri :   
         ya_existe=True  
         break  
     if ya_existe:   
       syslog (LOG_DEBUG, "Alta abortada, URI Repetido: %s" % device_uri)   
       return  
     #Fin de la comprobacion      
     uniquename = create_queue (c, printers, name, device_uris[0], ppdname,  
                   "%s %s" % (id_dict["MFG"], id_dict["MDL"]),  
                   installer)  
     if uniquename != None and fax_basename == False:  
       # Look for a corresponding fax queue. We can only  
       # identify these by looking for device URIs that are the  
       # same as this one but with a different scheme. If we  
       # find one whose scheme ends in "fax", use that as a fax  
       # queue. Note that the HPLIP backends do follow this  
       # pattern (hp and hpfax).  
       used_uris = map (lambda x: x.device_uri, printers.values ())  
       for uri in device_uris[1:]:  
         if uri.find (":") == -1:  
           continue  
         (scheme, rest) = uri.split (":", 1)  
         if scheme.endswith ("fax"):  
           # Now see if the non-scheme parts of the URI match  
           # any of the URIs we were given.  
           for each_uri in device_uris:  
             if each_uri == uri:  
               continue  
             (s, device_uri_rest) = each_uri.split (":", 1)  
             if rest == device_uri_rest:  
               # This one matches. Check there is not  
               # already a queue using this URI.  
               if uri in used_uris:  
                 break  
               try:  
                 devices = c.getDevices(include_schemes=[scheme])  
               except TypeError:  
                 # include_schemes requires pycups 1.9.46  
                 devices = c.getDevices ()  
               device_dict = devices.get (uri)  
               if device_dict == None:  
                 break  
               add_queue (device_dict.get ("device-id", ""),  
                     [uri], fax_basename=uniquename)  
   else:  
     # Not an exact match.  
     uniquename = device_uris[0]  
   if uniquename != None and notification:  
     try:  
       cmd = id_dict["CMD"]  
       if cmd:  
         cmd = reduce (lambda x, y: x + ',' + y, cmd)  
       else:  
         cmd = ""  
       notification.NewPrinter (status, uniquename, id_dict["MFG"],  
                    id_dict["MDL"], id_dict["DES"], cmd)  
     except dbus.DBusException, e:  
       syslog (LOG_DEBUG, "D-Bus method call failed: %s" % e)  
 if len (sys.argv) < 3:  
   print "Syntax: %s {Device ID} {Device URI} [other device URIs...]"  
   sys.exit (1)  
 openlog ("udev-add-printer", 0, LOG_LPR)  
 try:  
   add_queue (sys.argv[1], sys.argv[2:])  
 except SystemExit, e:  
   sys.exit (e)  
 except:  
   (type, value, tb) = sys.exc_info ()  
   tblast = traceback.extract_tb (tb, limit=None)  
   if len (tblast):  
     tblast = tblast[:len (tblast) - 1]  
   for line in traceback.format_tb (tb):  
     syslog (LOG_ERR, line.strip ())  
   extxt = traceback.format_exception_only (type, value)  
   syslog (LOG_ERR, extxt[0].strip ())  

Básicamente lo que hago es comprobar que el DeviceURI de la impresora no existe ya en la lista de impresoras previas, teniendo en cuenta que puede o no tener el prefijo del filtro "tea4cups://". Con esto estaremos a salvo de esas colas de impresión fantasma y tendremos la cola de impresión ajustada a la realidad.

A otra cosa, mariposa....


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