log: allow for message continuation

Some drivers use macro pr_cont() for continuing a message sent via printk.
Hence if we want to convert printk messaging to using the logging system,
we must support continuation of log messages too.

As pr_cont() does not provide a message level we need a means of
remembering the last log level.

With the patch a pseudo log level LOGL_CONT as well as a pseudo log
category LOGC_CONT are introduced. Using these results in the application
of the same log level and category as in the previous log message.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

common/log.c

@@ -191,10 +191,12 @@ static bool log_passes_filters(struct log_device *ldev, struct log_rec *rec)
  * log_dispatch() - Send a log record to all log devices for processing
  *
  * The log record is sent to each log device in turn, skipping those which have
- * filters which block the record
+ * filters which block the record.
  *
- * @rec: Log record to dispatch
+ * All log messages created while processing log record @rec are ignored.
- * @return 0 (meaning success)
+ *
+ * @rec:	log record to dispatch
+ * Return:	0 msg sent, 1 msg not sent while already dispatching another msg
  */
 static int log_dispatch(struct log_rec *rec)
 {
@@ -206,7 +208,7 @@ static int log_dispatch(struct log_rec *rec)
 	 * as this might result in infinite recursion.
 	 */
 	if (gd->processing_msg)
-		return 0;
+		return 1;
 
 	/* Emit message */
 	gd->processing_msg = true;
@@ -226,6 +228,12 @@ int _log(enum log_category_t cat, enum log_level_t level, const char *file,
 	struct log_rec rec;
 	va_list args;
 
+	/* Check for message continuation */
+	if (cat == LOGC_CONT)
+		cat = gd->logc_prev;
+	if (level == LOGL_CONT)
+		level = gd->logl_prev;
+
 	rec.cat = cat;
 	rec.level = level & LOGL_LEVEL_MASK;
 	rec.force_debug = level & LOGL_FORCE_DEBUG;
@@ -241,7 +249,10 @@ int _log(enum log_category_t cat, enum log_level_t level, const char *file,
 			gd->log_drop_count++;
 		return -ENOSYS;
 	}
-	log_dispatch(&rec);
+	if (!log_dispatch(&rec)) {
+		gd->logc_prev = cat;
+		gd->logl_prev = level;
+	}
 
 	return 0;
 }
@@ -381,6 +392,8 @@ int log_init(void)
 	if (!gd->default_log_level)
 		gd->default_log_level = CONFIG_LOG_DEFAULT_LEVEL;
 	gd->log_fmt = log_get_default_format();
+	gd->logc_prev = LOGC_NONE;
+	gd->logl_prev = LOGL_INFO;
 
 	return 0;
 }

doc/develop/logging.rst

@@ -38,6 +38,9 @@ There are a number logging levels available, in increasing order of verbosity:
 * LOGL_DEBUG_CONTENT - Debug message showing full message content
 * LOGL_DEBUG_IO - Debug message showing hardware I/O access
 
+To continue a log message in a separate call of function log() use
+
+* LOGL_CONT - Use same log level as in previous call
 
 Logging category
 ----------------
@@ -56,6 +59,9 @@ The following main categories are defined:
 * LOGC_DT - Related to device tree control
 * LOGC_EFI - Related to EFI implementation
 
+To continue a log message in a separate call of function log() use
+
+* LOGC_CONT - Use same category as in previous call
 
 Enabling logging
 ----------------

include/asm-generic/global_data.h

@@ -371,6 +371,18 @@ struct global_data {
 	 * while another message is being processed.
 	 */
 	bool processing_msg;
+	/**
+	 * @logc_prev: logging category of previous message
+	 *
+	 * This value is used as logging category for continuation messages.
+	 */
+	int logc_prev;
+	/**
+	 * @logl_pref: logging level of the previous message
+	 *
+	 * This value is used as logging level for continuation messages.
+	 */
+	int logl_prev;
 #endif
 #if CONFIG_IS_ENABLED(BLOBLIST)
 	/**

include/log.h

@@ -38,6 +38,7 @@ enum log_level_t {
 
 	LOGL_FIRST = LOGL_EMERG,
 	LOGL_MAX = LOGL_DEBUG_IO,
+	LOGL_CONT = -1,		/* Use same log level as in previous call */
 };
 
 /**
@@ -65,6 +66,7 @@ enum log_category_t {
 
 	LOGC_COUNT,	/* Number of log categories */
 	LOGC_END,	/* Sentinel value for a list of log categories */
+	LOGC_CONT = -1,	/* Use same category as in previous call */
 };
 
 /* Helper to cast a uclass ID to a log category */