db: add ring buffer for DB query

This patch adds an optional ring buffer option which modify
the way database queries are made. The main thread is only handling
kernel message reading and query formatting. The SQL request is made
in a separate dedicated thread.
The idea is to try to avoid buffer overrun by minimizing the time
requested to treat kernel message. Doing synchronous SQL request, as
it was made before was causing a delay which could cause some messages
to be lost in case of burst from kernel side.

1 files changed, 30 insertions, 1 deletions

diff --git a/include/ulogd/db.h b/include/ulogd/db.h
index 82f37b9..e9b054b 100644
--- a/include/ulogd/db.h
+++ b/include/ulogd/db.h
@@ -21,6 +21,24 @@ struct db_driver {
 			const char *stmt, unsigned int len);
 };
 
+enum {
+	RING_NO_QUERY,
+	RING_QUERY_READY,
+};
+
+struct db_stmt_ring {
+	/* Ring buffer: 1 status byte + string */
+	char *ring; /* pointer to the ring */
+	uint32_t size; /* size of ring buffer in element */
+	int length; /* length of one ring buffer element */
+	uint32_t wr_item; /* write item in ring buffer */
+	uint32_t rd_item; /* read item in ring buffer */
+	char *wr_place;
+	pthread_cond_t cond;
+	pthread_mutex_t mutex;
+	int full;
+};
+
 struct db_stmt {
 	char *stmt;
 	int len;
@@ -34,6 +52,10 @@ struct db_instance {
 	time_t reconnect;
 	int (*interp)(struct ulogd_pluginstance *upi);
 	struct db_driver *driver;
+	/* DB ring buffer */
+	struct db_stmt_ring ring;
+	pthread_t db_thread_id;
+	/* Backlog system */
 	unsigned int backlog_memcap;
 	unsigned int backlog_memusage;
 	unsigned int backlog_oneshot;
@@ -43,6 +65,7 @@ struct db_instance {
 #define TIME_ERR		((time_t)-1)	/* Be paranoid */
 #define RECONNECT_DEFAULT	2
 #define MAX_ONESHOT_REQUEST	10
+#define RING_BUFFER_DEFAULT_SIZE	10
 
 #define DB_CES							\
 		{						\
@@ -73,15 +96,21 @@ struct db_instance {
 			.key = "backlog_oneshot_requests",	\
 			.type = CONFIG_TYPE_INT,		\
 			.u.value = MAX_ONESHOT_REQUEST,		\
+		},						\
+		{						\
+			.key = "ring_buffer_size",		\
+			.type = CONFIG_TYPE_INT,		\
+			.u.value = RING_BUFFER_DEFAULT_SIZE,	\
 		}
 
-#define DB_CE_NUM		6
+#define DB_CE_NUM		7
 #define table_ce(x)		(x->ces[0])
 #define reconnect_ce(x)		(x->ces[1])
 #define timeout_ce(x)		(x->ces[2])
 #define procedure_ce(x)		(x->ces[3])
 #define backlog_memcap_ce(x)	(x->ces[4])
 #define backlog_oneshot_ce(x)	(x->ces[5])
+#define ringsize_ce(x)		(x->ces[6])
 
 void ulogd_db_signal(struct ulogd_pluginstance *upi, int signal);
 int ulogd_db_start(struct ulogd_pluginstance *upi);