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>

2 files changed, 11 insertions, 1 deletions

diff --git a/source3/rpc_server/spoolss/srv_spoolss_nt.c b/source3/rpc_server/spoolss/srv_spoolss_nt.c
index 760c924d80..b8cae89e97 100644
--- a/source3/rpc_server/spoolss/srv_spoolss_nt.c
+++ b/source3/rpc_server/spoolss/srv_spoolss_nt.c
@@ -4312,7 +4312,7 @@ static WERROR enum_all_printers_info_level(TALLOC_CTX *mem_ctx,
 					   uint32_t *count_p)
 {
 	int snum;
-	int n_services = lp_numservices();
+	int n_services;
 	union spoolss_PrinterInfo *info = NULL;
 	uint32_t count = 0;
 	WERROR result = WERR_OK;
@@ -4324,6 +4324,15 @@ static WERROR enum_all_printers_info_level(TALLOC_CTX *mem_ctx,
 		return WERR_NOMEM;
 	}
 
+	/*
+	 * printer shares are only updated on client enumeration. The background
+	 * printer process updates printer_list.tdb at regular intervals.
+	 */
+	become_root();
+	delete_and_reload_printers(server_event_context(), msg_ctx);
+	unbecome_root();
+
+	n_services = lp_numservices();
 	*count_p = 0;
 	*info_p = NULL;
 
diff --git a/source3/rpc_server/srvsvc/srv_srvsvc_nt.c b/source3/rpc_server/srvsvc/srv_srvsvc_nt.c
index e030b98ad0..11abc6c838 100644
--- a/source3/rpc_server/srvsvc/srv_srvsvc_nt.c
+++ b/source3/rpc_server/srvsvc/srv_srvsvc_nt.c
@@ -548,6 +548,7 @@ static WERROR init_srv_share_info_ctr(struct pipes_struct *p,
 
 	/* Ensure all the usershares are loaded. */
 	become_root();
+	delete_and_reload_printers(server_event_context(), p->msg_ctx);
 	load_usershare_shares(NULL, connections_snum_used);
 	load_registry_shares();
 	num_services = lp_numservices();