log: Add a flag to enable log drivers

At present there is no way to disable a log driver. But the syslog driver
causes (attempted) network traffic in sandbox every time a log message
is printed, which is often.

Add a flag to enable a log driver. Adjust struct log_device to use a short
for next_filter_num so that no more memory is used for devices. Also fix
a missing line in the struct log_driver comment while here.

To maintain compatibility, enable it for all drivers for now.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/log.c

@@ -207,7 +207,8 @@ static int log_dispatch(struct log_rec *rec)
 	/* Emit message */
 	processing_msg = 1;
 	list_for_each_entry(ldev, &gd->log_head, sibling_node) {
-		if (log_passes_filters(ldev, rec))
+		if ((ldev->flags & LOGDF_ENABLE) &&
+		    log_passes_filters(ldev, rec))
 			ldev->drv->emit(ldev, rec);
 	}
 	processing_msg = 0;
@@ -329,6 +330,7 @@ int log_init(void)
 		}
 		INIT_LIST_HEAD(&ldev->filter_head);
 		ldev->drv = drv;
+		ldev->flags = drv->flags;
 		list_add_tail(&ldev->sibling_node,
 			      (struct list_head *)&gd->log_head);
 		drv++;

common/log_console.c

@@ -44,4 +44,5 @@ static int log_console_emit(struct log_device *ldev, struct log_rec *rec)
 LOG_DRIVER(console) = {
 	.name	= "console",
 	.emit	= log_console_emit,
+	.flags	= LOGDF_ENABLE,
 };

common/log_syslog.c

@@ -107,4 +107,5 @@ out:
 LOG_DRIVER(syslog) = {
 	.name	= "syslog",
 	.emit	= log_syslog_emit,
+	.flags	= LOGDF_ENABLE,
 };

include/log.h

@@ -307,10 +307,16 @@ struct log_rec {
 
 struct log_device;
 
+enum log_device_flags {
+	LOGDF_ENABLE		= BIT(0),	/* Device is enabled */
+};
+
 /**
  * struct log_driver - a driver which accepts and processes log records
  *
  * @name: Name of driver
+ * @emit: Method to call to emit a log record via this device
+ * @flags: Initial value for flags (use LOGDF_ENABLE to enable on start-up)
  */
 struct log_driver {
 	const char *name;
@@ -321,6 +327,7 @@ struct log_driver {
 	 * for processing. The filter is checked before calling this function.
 	 */
 	int (*emit)(struct log_device *ldev, struct log_rec *rec);
+	unsigned short flags;
 };
 
 /**
@@ -333,12 +340,14 @@ struct log_driver {
  * @next_filter_num: Seqence number of next filter filter added (0=no filters
  *	yet). This increments with each new filter on the device, but never
  *	decrements
+ * @flags: Flags for this filter (enum log_device_flags)
  * @drv: Pointer to driver for this device
  * @filter_head: List of filters for this device
  * @sibling_node: Next device in the list of all devices
  */
 struct log_device {
-	int next_filter_num;
+	unsigned short next_filter_num;
+	unsigned short flags;
 	struct log_driver *drv;
 	struct list_head filter_head;
 	struct list_head sibling_node;