printload: add a column for the number of used file descriptors

And the maximum number of configured file descriptors.

Note that this is per group, not per thread, so that e.g. logger and
log_writer_file show the same number.

src/modules/systemlib/printload.c

@@ -133,7 +133,7 @@ void print_load_buffer(uint64_t t, char *buffer, int buffer_length, print_load_c
 		print_state->interval_time_ms_inv = 1.f / ((float)((print_state->new_time - print_state->interval_start_time) / 1000));
 
 		/* header for task list */
-		snprintf(buffer, buffer_length, "%4s %*-s %8s %6s %11s %10s %-6s",
+		snprintf(buffer, buffer_length, "%4s %*-s %8s %6s %11s %10s %-5s %2s",
 			 "PID",
 			 CONFIG_TASK_NAME_SIZE, "COMMAND",
 			 "CPU(ms)",
@@ -141,10 +141,11 @@ void print_load_buffer(uint64_t t, char *buffer, int buffer_length, print_load_c
 			 "USED/STACK",
 			 "PRIO(BASE)",
 #if CONFIG_RR_INTERVAL > 0
-			 "TSLICE"
+			 "TSLICE",
 #else
-			 "STATE"
+			 "STATE",
 #endif
+			 "FD"
 			);
 		cb(user);
 
@@ -201,6 +202,19 @@ void print_load_buffer(uint64_t t, char *buffer, int buffer_length, print_load_c
 		unsigned tcb_task_state = system_load.tasks[i].tcb->task_state;
 		unsigned tcb_sched_priority = system_load.tasks[i].tcb->sched_priority;
 
+		unsigned int tcb_num_used_fds = 0; // number of used file descriptors
+#if CONFIG_NFILE_DESCRIPTORS > 0
+		FAR struct task_group_s *group = system_load.tasks[i].tcb->group;
+
+		if (group) {
+			for (int fd_index = 0; fd_index < CONFIG_NFILE_DESCRIPTORS; ++fd_index) {
+				if (group->tg_filelist.fl_files[fd_index].f_inode) {
+					++tcb_num_used_fds;
+				}
+			}
+		}
+
+#endif
 
 		sched_unlock();
 
@@ -270,11 +284,11 @@ void print_load_buffer(uint64_t t, char *buffer, int buffer_length, print_load_c
 #endif
 #if CONFIG_RR_INTERVAL > 0
 		/* print scheduling info with RR time slice */
-		snprintf(buffer + print_len, buffer_length - print_len, " %6d", tcb_timeslice);
+		snprintf(buffer + print_len, buffer_length - print_len, " %5d %2d", tcb_timeslice, tcb_num_used_fds);
 		(void)tstate_name(TSTATE_TASK_INVALID); // Stop not used warning
 #else
 		// print task state instead
-		snprintf(buffer + print_len, buffer_length - print_len, " %-6s", tstate_name(tcb_task_state));
+		snprintf(buffer + print_len, buffer_length - print_len, " %-5s %2d", tstate_name(tcb_task_state), tcb_num_used_fds);
 #endif
 		cb(user);
 	}
@@ -300,10 +314,11 @@ void print_load_buffer(uint64_t t, char *buffer, int buffer_length, print_load_c
 
 	sched_load = 1.f - idle_load - task_load;
 
-	snprintf(buffer, buffer_length, "Processes: %d total, %d running, %d sleeping",
+	snprintf(buffer, buffer_length, "Processes: %d total, %d running, %d sleeping, max FDs: %d",
 		 system_load.total_count,
 		 print_state->running_count,
-		 print_state->blocked_count);
+		 print_state->blocked_count,
+		 CONFIG_NFILE_DESCRIPTORS);
 	cb(user);
 	snprintf(buffer, buffer_length, "CPU usage: %.2f%% tasks, %.2f%% sched, %.2f%% idle",
 		 (double)(task_load * 100.f),