logging: Add option to have tag which is prepended to all messages

Tag can be changed at runtime. Feature is enabled by setting
maximum tag length to positive value. Additionally, default
tag can be configured in Kconfig.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>

include/logging/log_ctrl.h

@@ -210,6 +210,17 @@ static inline bool log_data_pending(void)
 	return false;
 }
 
+/**
+ * @brief Configure tag used to prefix each message.
+ *
+ * @param tag Tag.
+ *
+ * @retval 0 on successful operation.
+ * @retval -ENOTSUP if feature is disabled.
+ * @retval -ENOMEM if string is longer than the buffer capacity. Tag will be trimmed.
+ */
+int log_set_tag(const char *tag);
+
 #if defined(CONFIG_LOG) && !defined(CONFIG_LOG_MODE_MINIMAL)
 #define LOG_CORE_INIT() log_core_init()
 #define LOG_INIT() log_init()

include/logging/log_internal.h

@@ -95,6 +95,12 @@ void z_log_msg2_free(union log_msg2_generic *msg);
  */
 bool z_log_msg2_pending(void);
 
+/** @brief Get tag.
+ *
+ * @return Tag. Null if feature is disabled.
+ */
+const char *z_log_get_tag(void);
+
 #ifdef __cplusplus
 }
 #endif

subsys/logging/Kconfig.formatting

@@ -63,7 +63,22 @@ if LOG_BACKEND_SHOW_COLOR
 config LOG_INFO_COLOR_GREEN
 	bool "Use green color for info level logs"
 
-endif
+endif # LOG_BACKEND_SHOW_COLOR
+
+config LOG_TAG_MAX_LEN
+	int "Tag max length"
+	default 0
+	range 0 64
+	help
+	  Setting non-zero value enables option to specify a tag which is
+	  prepended to each log message. Tag can be changed at runtime.
+
+config LOG_TAG_DEFAULT
+	string "Default tag"
+	depends on LOG_TAG_MAX_LEN > 0
+	default ""
+	help
+	  Initial tag.
 
 config LOG_BACKEND_FORMAT_TIMESTAMP
 	bool "Enable timestamp formatting in the backend"

subsys/logging/log_core.c

@@ -109,6 +109,14 @@ static const struct mpsc_pbuf_buffer_config mpsc_config = {
 		MPSC_PBUF_MODE_OVERWRITE : 0
 };
 
+/* Check that default tag can fit in tag buffer. */
+COND_CODE_0(CONFIG_LOG_TAG_MAX_LEN, (),
+	(BUILD_ASSERT(sizeof(CONFIG_LOG_TAG_DEFAULT) <= CONFIG_LOG_TAG_MAX_LEN + 1,
+		      "Default string longer than tag capacity")));
+
+static char tag[CONFIG_LOG_TAG_MAX_LEN + 1] =
+	COND_CODE_0(CONFIG_LOG_TAG_MAX_LEN, ({}), (CONFIG_LOG_TAG_DEFAULT));
+
 bool log_is_strdup(const void *buf);
 static void msg_process(union log_msgs msg, bool bypass);
 
@@ -1215,6 +1223,35 @@ bool z_log_msg2_pending(void)
 	return mpsc_pbuf_is_pending(&log_buffer);
 }
 
+const char *z_log_get_tag(void)
+{
+	return CONFIG_LOG_TAG_MAX_LEN > 0 ? tag : NULL;
+}
+
+int log_set_tag(const char *str)
+{
+	if (CONFIG_LOG_TAG_MAX_LEN == 0) {
+		return -ENOTSUP;
+	}
+
+	if (str == NULL) {
+		return -EINVAL;
+	}
+
+	size_t len = strlen(str);
+	size_t cpy_len = MIN(len, CONFIG_LOG_TAG_MAX_LEN);
+
+	memcpy(tag, str, cpy_len);
+	tag[cpy_len] = '\0';
+
+	if (cpy_len < len) {
+		tag[cpy_len - 1] = '~';
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
 static void log_process_thread_timer_expiry_fn(struct k_timer *timer)
 {
 	k_sem_give(&log_process_thread_sem);

subsys/logging/log_output.c

@@ -495,6 +495,7 @@ static uint32_t prefix_print(const struct log_output *output,
 	bool stamp = flags & LOG_OUTPUT_FLAG_TIMESTAMP;
 	bool colors_on = flags & LOG_OUTPUT_FLAG_COLORS;
 	bool level_on = flags & LOG_OUTPUT_FLAG_LEVEL;
+	const char *tag = z_log_get_tag();
 
 	if (IS_ENABLED(CONFIG_LOG_BACKEND_NET) &&
 	    flags & LOG_OUTPUT_FLAG_FORMAT_SYSLOG) {
@@ -512,6 +513,10 @@ static uint32_t prefix_print(const struct log_output *output,
 			level_to_rfc5424_severity(level));
 	}
 
+	if (tag) {
+		length += print_formatted(output, "%s ", tag);
+	}
+
 	if (stamp) {
 		length += timestamp_print(output, flags, timestamp);
 	}