printing: only reload printer shares on client enum

Currently, automatic printer share updates are handled in the following
way:
- Background printer process (BPP) forked on startup
- Parent smbd and per-client children await MSG_PRINTER_PCAP messages
- BPP periodically polls the printing backend for printcap data
	- printcap data written to printer_list.tdb
	- MSG_PRINTER_PCAP sent to all smbd processes following update
- smbd processes all read the latest printer_list.tdb data, and update
  their share listings

This procedure is not scalable, as all smbd processes hit
printer_list.tdb in parallel, resulting in a large spike in CPU usage.

This change sees smbd processes only update their printer share lists
only when a client asks for this information, e.g. via NetShareEnum or
EnumPrinters.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=10652

Suggested-by: Volker Lendecke <vl@samba.org>
Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>

1 files changed, 5 insertions, 29 deletions

diff --git a/source3/printing/spoolssd.c b/source3/printing/spoolssd.c
index f181fcc3f2f..afb8f4fd2fe 100644
--- a/source3/printing/spoolssd.c
+++ b/source3/printing/spoolssd.c
@@ -132,27 +132,6 @@ static void smb_conf_updated(struct messaging_context *msg,
 	update_conf(ev_ctx, msg);
 }
 
-static void update_pcap(struct tevent_context *ev_ctx,
-			struct messaging_context *msg_ctx)
-{
-	change_to_root_user();
-	delete_and_reload_printers(ev_ctx, msg_ctx);
-}
-
-static void pcap_updated(struct messaging_context *msg,
-			 void *private_data,
-			 uint32_t msg_type,
-			 struct server_id server_id,
-			 DATA_BLOB *data)
-{
-	struct tevent_context *ev_ctx;
-
-	ev_ctx = talloc_get_type_abort(private_data, struct tevent_context);
-
-	DEBUG(10, ("Got message that pcap updated. Reloading.\n"));
-	update_pcap(ev_ctx, msg);
-}
-
 static void spoolss_sig_term_handler(struct tevent_context *ev,
 				     struct tevent_signal *se,
 				     int signum,
@@ -318,8 +297,6 @@ static bool spoolss_child_init(struct tevent_context *ev_ctx,
 
 	messaging_register(msg_ctx, ev_ctx,
 			   MSG_SMB_CONF_UPDATED, smb_conf_updated);
-	messaging_register(msg_ctx, ev_ctx, MSG_PRINTER_PCAP,
-			   pcap_updated);
 	messaging_register(msg_ctx, ev_ctx,
 			   MSG_PREFORK_PARENT_EVENT, parent_ping);
 
@@ -739,15 +716,14 @@ pid_t start_spoolssd(struct tevent_context *ev_ctx,
 			   MSG_SMB_CONF_UPDATED, smb_conf_updated);
 	messaging_register(msg_ctx, NULL, MSG_PRINTER_UPDATE,
 			   print_queue_forward);
-	messaging_register(msg_ctx, ev_ctx, MSG_PRINTER_PCAP,
-			   pcap_updated);
 	messaging_register(msg_ctx, ev_ctx,
 			   MSG_PREFORK_CHILD_EVENT, child_ping);
 
-	/* As soon as messaging is up check if pcap has been loaded already.
-	 * If so then we probably missed a message and should load_printers()
-	 * ourselves. If pcap has not been loaded yet, then ignore, we will get
-	 * a message as soon as the bq process completes the reload. */
+	/*
+	 * As soon as messaging is up check if pcap has been loaded already.
+	 * If pcap has not been loaded yet, then ignore, as we will reload on
+	 * client enumeration anyway.
+	 */
 	if (pcap_cache_loaded()) {
 		load_printers(ev_ctx, msg_ctx);
 	}