logger: add SDLOG_DIRS_MAX param to limit the max number of log directories

Disabled by default, so that logs are not deleted unexpectedly.

src/modules/logger/logger.cpp

@@ -399,6 +399,7 @@ Logger::Logger(LogWriter::Backend backend, size_t buffer_size, uint32_t log_inte
 	_sdlog_mode(0)
 {
 	_log_utc_offset = param_find("SDLOG_UTC_OFFSET");
+	_log_dirs_max = param_find("SDLOG_DIRS_MAX");
 	_sdlog_mode_handle = param_find("SDLOG_MODE");
 
 	if (poll_topic_name) {
@@ -1770,6 +1771,16 @@ int Logger::check_free_space()
 {
 	struct statfs statfs_buf;
 
+	int32_t max_log_dirs_to_keep = 0;
+
+	if (_log_dirs_max != PARAM_INVALID) {
+		param_get(_log_dirs_max, &max_log_dirs_to_keep);
+	}
+
+	if (max_log_dirs_to_keep == 0) {
+		max_log_dirs_to_keep = INT32_MAX;
+	}
+
 	/* remove old logs if the free space falls below a threshold */
 	do {
 		if (statfs(LOG_ROOT, &statfs_buf) != 0) {
@@ -1838,8 +1849,9 @@ int Logger::check_free_space()
 			min_free_bytes = total_bytes / 10;
 		}
 
-		if (statfs_buf.f_bavail >= (px4_statfs_buf_f_bavail_t)(min_free_bytes / statfs_buf.f_bsize)) {
-			break; // enough free space
+		if (num_sess + num_dates <= max_log_dirs_to_keep &&
+		    statfs_buf.f_bavail >= (px4_statfs_buf_f_bavail_t)(min_free_bytes / statfs_buf.f_bsize)) {
+			break; // enough free space and limit not reached
 		}
 
 		if (num_sess == 0 && num_dates == 0) {
@@ -1873,7 +1885,7 @@ int Logger::check_free_space()
 	} while (true);
 
 
-	/* use a threshold of 50 MiB */
+	/* use a threshold of 50 MiB: if below, do not start logging */
 	if (statfs_buf.f_bavail < (px4_statfs_buf_f_bavail_t)(50 * 1024 * 1024 / statfs_buf.f_bsize)) {
 		mavlink_log_critical(&_mavlink_log_pub,
 				     "[logger] Not logging; SD almost full: %u MiB",

src/modules/logger/logger.h

@@ -289,6 +289,7 @@ private:
 	uint32_t					_log_interval;
 	const orb_metadata				*_polling_topic_meta = nullptr; ///< if non-null, poll on this topic instead of sleeping
 	param_t						_log_utc_offset;
+	param_t						_log_dirs_max;
 	orb_advert_t					_mavlink_log_pub = nullptr;
 	uint16_t					_next_topic_id = 0; ///< id of next subscribed ulog topic
 	char						*_replay_file_name = nullptr;

src/modules/logger/params.c

@@ -69,6 +69,25 @@ PARAM_DEFINE_INT32(SDLOG_UTC_OFFSET, 0);
  */
 PARAM_DEFINE_INT32(SDLOG_MODE, 0);
 
+/**
+ * Maximum number of log directories to keep
+ *
+ * If there are more log directories than this value,
+ * the system will delete the oldest directories during startup.
+ *
+ * In addition, the system will delete old logs if there is not enough free space left.
+ * The minimum amount is 300 MB.
+ *
+ * If this is set to 0, old directories will only be removed if the free space falls below
+ * the minimum.
+ *
+ * @min 0
+ * @max 1000
+ * @reboot_required true
+ * @group SD Logging
+ */
+PARAM_DEFINE_INT32(SDLOG_DIRS_MAX, 0);
+
 /**
  * Log UUID
  *