bonefish + mmlr:

* Add possibility to restart a complete pipe through B_KDEBUG_RESTART_PIPE.
* Implement tail in the kernel debugger making use of the former.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@28154 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/debug.h

@@ -48,7 +48,8 @@
 #endif
 
 // command return value
-#define B_KDEBUG_ERROR	4
+#define B_KDEBUG_ERROR			4
+#define B_KDEBUG_RESTART_PIPE	5
 
 // command flags
 #define B_KDEBUG_DONT_PARSE_ARGUMENTS	(0x01)

src/system/kernel/debug/debug_builtin_commands.cpp

@@ -148,6 +148,59 @@ cmd_head(int argc, char** argv)
 }
 
 
+static int
+cmd_tail(int argc, char** argv)
+{
+	debugger_command_pipe_segment* segment
+		= get_current_debugger_command_pipe_segment();
+	if (segment == NULL) {
+		kprintf_unfiltered("%s can only be run as part of a pipe!\n", argv[0]);
+		return B_KDEBUG_ERROR;
+	}
+
+	struct user_data {
+		uint64	max_lines;
+		int64	line_count;
+		bool	restarted;
+	};
+	user_data* userData = (user_data*)segment->user_data;
+
+	if (segment->invocations == 0) {
+		if (argc > 3) {
+			print_debugger_command_usage(argv[0]);
+			return B_KDEBUG_ERROR;
+		}
+
+		userData->max_lines = 10;
+		if (argc > 2 && !evaluate_debug_expression(argv[1],
+				&userData->max_lines, false)) {
+			return B_KDEBUG_ERROR;
+		}
+
+		userData->line_count = 1;
+		userData->restarted = false;
+	} else if (!userData->restarted) {
+		if (argv[argc - 1] == NULL) {
+			userData->restarted = true;
+			userData->line_count -= userData->max_lines;
+			return B_KDEBUG_RESTART_PIPE;
+		}
+
+		++userData->line_count;
+	} else {
+		if (argv[argc - 1] == NULL)
+			return 0;
+
+		if (--userData->line_count < 0) {
+			kputs(argv[argc - 1]);
+			kputs("\n");
+		}
+	}
+
+	return 0;
+}
+
+
 static int
 cmd_grep(int argc, char** argv)
 {
@@ -300,6 +353,13 @@ debug_builtin_commands_init()
 		"Should be used in a command pipe. It prints only the first\n"
 		"<maxLines> lines of output from the previous command in the pipe and\n"
 		"silently discards the rest of the output.\n", 0);
+	add_debugger_command_etc("tail", &cmd_tail,
+		"Prints only the last lines of output from another command",
+		"[ <maxLines> ]\n"
+		"Should be used in a command pipe. It prints only the last\n"
+		"<maxLines> (default 10) lines of output from the previous command in\n"
+		"the pipe and silently discards the rest of the output.\n",
+		B_KDEBUG_PIPE_FINAL_RERUN);
 	add_debugger_command_etc("grep", &cmd_grep,
 		"Filters output from another command",
 		"[ -i ] [ -v ] <pattern>\n"

src/system/kernel/debug/debug_commands.cpp

@@ -351,13 +351,25 @@ invoke_debugger_command_pipe(debugger_command_pipe* pipe)
 			sOutputBuffers[i], kOutputBufferSize);
 	}
 
-	int result = invoke_pipe_segment(pipe, 0, NULL);
+	int result;
+	while (true) {
+		result = invoke_pipe_segment(pipe, 0, NULL);
 
-	// perform final rerun for all commands that want it
-	for (int32 i = 1; result != B_KDEBUG_ERROR && i < segments; i++) {
-		debugger_command_pipe_segment& segment = pipe->segments[i];
-		if ((segment.command->flags & B_KDEBUG_PIPE_FINAL_RERUN) != 0)
-			result = invoke_pipe_segment(pipe, i, NULL);
+		// perform final rerun for all commands that want it
+		for (int32 i = 1; result != B_KDEBUG_ERROR && i < segments; i++) {
+			debugger_command_pipe_segment& segment = pipe->segments[i];
+			if ((segment.command->flags & B_KDEBUG_PIPE_FINAL_RERUN) != 0) {
+				result = invoke_pipe_segment(pipe, i, NULL);
+				if (result == B_KDEBUG_RESTART_PIPE) {
+					for (int32 j = 0; j < i; j++)
+						pipe->segments[j].invocations = 0;
+					break;
+				}
+			}
+		}
+
+		if (result != B_KDEBUG_RESTART_PIPE)
+			break;
 	}
 
 	sCurrentPipe = oldPipe;