s3: printing: Fix problem with server taking too long to respond to a MSG_PRINTER_DRVUPGRADE message.

Receiving a MSG_PRINTER_DRVUPGRADE causes
smbd to iterate over all printers looking
for ones that uses the driver. This is a very
expensive operation requiring a read of all
registry printer parameters.

On a system with a large number of printers,
this causes the clients to timeout (smbd
can take longer than 60 seconds to respond).

This patch fixes the problem by forwarding
the MSG_PRINTER_DRVUPGRADE to the background
lpq queue updater process and allowing it to
take care of the updating of the changeid
in the registry, allowing the smbd connected
to the client to return to processing requests
immediately.

https://bugzilla.samba.org/show_bug.cgi?id=9942

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>

Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Tue Feb 18 17:48:30 CET 2014 on sn-devel-104

3 files changed, 34 insertions, 2 deletions

diff --git a/source3/printing/nt_printing.c b/source3/printing/nt_printing.c
index 376dcfafa8..6a5f2d744a 100644
--- a/source3/printing/nt_printing.c
+++ b/source3/printing/nt_printing.c
@@ -132,6 +132,31 @@ static bool print_driver_directories_init(void)
 }
 
 /****************************************************************************
+ Forward a MSG_PRINTER_DRVUPGRADE message from another smbd to the
+ background lpq updater.
+****************************************************************************/
+
+static void forward_drv_upgrade_printer_msg(struct messaging_context *msg,
+				void *private_data,
+				uint32_t msg_type,
+				struct server_id server_id,
+				DATA_BLOB *data)
+{
+	extern pid_t background_lpq_updater_pid;
+
+	if (background_lpq_updater_pid == -1) {
+		DEBUG(3,("no background lpq queue updater\n"));
+		return;
+	}
+
+	messaging_send_buf(msg,
+			pid_to_procid(background_lpq_updater_pid),
+			MSG_PRINTER_DRVUPGRADE,
+			data->data,
+			data->length);
+}
+
+/****************************************************************************
  Open the NT printing tdbs. Done once before fork().
 ****************************************************************************/
 
@@ -149,10 +174,10 @@ bool nt_printing_init(struct messaging_context *msg_ctx)
 
 	/*
 	 * register callback to handle updating printers as new
-	 * drivers are installed
+	 * drivers are installed. Forwards to background lpq updater.
 	 */
 	messaging_register(msg_ctx, NULL, MSG_PRINTER_DRVUPGRADE,
-			   do_drv_upgrade_printer);
+			forward_drv_upgrade_printer_msg);
 
 	/* of course, none of the message callbacks matter if you don't
 	   tell messages.c that you interested in receiving PRINT_GENERAL
diff --git a/source3/printing/queue_process.c b/source3/printing/queue_process.c
index bc6c33f9a8..aa0d0fb6a8 100644
--- a/source3/printing/queue_process.c
+++ b/source3/printing/queue_process.c
@@ -32,6 +32,7 @@
 #include "smbd/smbd.h"
 #include "rpc_server/rpc_config.h"
 #include "printing/load.h"
+#include "rpc_server/spoolss/srv_spoolss_nt.h"
 
 extern pid_t start_spoolssd(struct tevent_context *ev_ctx,
 			    struct messaging_context *msg_ctx);
@@ -314,6 +315,11 @@ pid_t start_background_queue(struct tevent_context *ev,
 				   bq_smb_conf_updated);
 		messaging_register(msg_ctx, NULL, MSG_PRINTER_UPDATE,
 				   print_queue_receive);
+		/* Remove previous forwarder message set in parent. */
+		messaging_deregister(msg_ctx, MSG_PRINTER_DRVUPGRADE, NULL);
+
+		messaging_register(msg_ctx, NULL, MSG_PRINTER_DRVUPGRADE,
+				   do_drv_upgrade_printer);
 
 		fde = tevent_add_fd(ev, ev, pause_pipe[1], TEVENT_FD_READ,
 				    printing_pause_fd_handler,
diff --git a/source3/rpc_server/spoolss/srv_spoolss_nt.c b/source3/rpc_server/spoolss/srv_spoolss_nt.c
index dc90b7708e..1305b1006e 100644
--- a/source3/rpc_server/spoolss/srv_spoolss_nt.c
+++ b/source3/rpc_server/spoolss/srv_spoolss_nt.c
@@ -1515,6 +1515,7 @@ void srv_spoolss_cleanup(void)
 /**********************************************************************
  callback to receive a MSG_PRINTER_DRVUPGRADE message and interate
  over all printers, upgrading ones as necessary
+ This is now *ONLY* called inside the background lpq updater. JRA.
  **********************************************************************/
 
 void do_drv_upgrade_printer(struct messaging_context *msg,