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From: Edward Tomasz Napierala <trasz@FreeBSD.org>
Date: Thu, 6 Jul 2017 12:27:14 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: svn commit: r320733 - head/sys/ddb
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Author: trasz
Date: Thu Jul  6 12:27:14 2017
New Revision: 320733
URL: https://svnweb.freebsd.org/changeset/base/320733

Log:
  Make ddb(4) a bit more user-friendly by improving "help".
  
  Obtained from:	CheriBSD
  MFC after:	2 weeks
  Sponsored by:	DARPA, AFRL

Modified:
  head/sys/ddb/db_command.c

Modified: head/sys/ddb/db_command.c
==============================================================================
--- head/sys/ddb/db_command.c	Thu Jul  6 12:19:15 2017	(r320732)
+++ head/sys/ddb/db_command.c	Thu Jul  6 12:27:14 2017	(r320733)
@@ -325,11 +325,26 @@ static void
 db_cmd_list(struct command_table *table)
 {
 	struct command	*cmd;
+	int have_subcommands;
 
+	have_subcommands = 0;
 	LIST_FOREACH(cmd, table, next) {
+		if (cmd->more != NULL)
+			have_subcommands++;
 		db_printf("%-16s", cmd->name);
 		db_end_line(16);
 	}
+
+	if (have_subcommands > 0) {
+		db_printf("\nThe following have subcommands; append \"help\" "
+		    "to list (e.g. \"show help\"):\n");
+		LIST_FOREACH(cmd, table, next) {
+			if (cmd->more == NULL)
+				continue;
+			db_printf("%-16s", cmd->name);
+			db_end_line(16);
+		}
+	}
 }
 
 static void
@@ -371,7 +386,8 @@ db_command(struct command **last_cmdp, struct command_
 				       &cmd);
 		switch (result) {
 		    case CMD_NONE:
-			db_printf("No such command\n");
+			db_printf("No such command; use \"help\" "
+			    "to list available commands\n");
 			db_flush_lex();
 			return;
 		    case CMD_AMBIGUOUS:
@@ -379,6 +395,13 @@ db_command(struct command **last_cmdp, struct command_
 			db_flush_lex();
 			return;
 		    case CMD_HELP:
+			if (cmd_table == &db_cmd_table) {
+			    db_printf("This is ddb(4), the kernel debugger; "
+			        "see http://man.freebsd.org/ddb/4 for help.\n");
+			    db_printf("Use \"bt\" for backtrace, \"dump\" for "
+			        "kernel core dump, \"reset\" to reboot.\n");
+			    db_printf("Available commands:\n");
+			}
 			db_cmd_list(cmd_table);
 			db_flush_lex();
 			return;
@@ -388,6 +411,8 @@ db_command(struct command **last_cmdp, struct command_
 		if ((cmd_table = cmd->more) != NULL) {
 		    t = db_read_token();
 		    if (t != tIDENT) {
+			db_printf("Subcommand required; "
+			    "available subcommands:\n");
 			db_cmd_list(cmd_table);
 			db_flush_lex();
 			return;