Re: [PATCH] monitor: Add `clear` command

["Dr. David Alan Gilbert" <dave@treblig.org>]

* Alano Song (alanosong@163.com) wrote:
> At 2026-04-19 01:23:46, "Dr. David Alan Gilbert" <dave@treblig.org> wrote:
> >* AlanoSong@163.com (AlanoSong@163.com) wrote:
> >> The monitor screen can be cluttered after executing commands
> >> like `info qtree`. It is useful to have a command to clear
> >> current screen, just like linux `clear` command do.
> >> 
> >> This patch has been tested under monitors using stdio, vc,
> >> tcp socket, unix socket and serial interfaces.
> >> 
> >> Signed-off-by: Alano Song <AlanoSong@163.com>
> >
> >Does typing ctrl-l not do it for you in your terminal?
> >
> >Dave
> >

Hi Alano,

> Yes, you are correct that ctrl-l provides basic screen clear,
> but the new `clear` command clears both visible screen and
> scrollback buffer, just like `clear` command does on my Ubuntu terminal.

> I still believe that this patch is useful:
> 1) Many linux users like me instinctively type `clear`
> when we want to tidy up the terminal.
> 2) Not everyone is aware of or remembers the ctrl-l shortcut.
>    A typed command is more discoverable, especially for new users
>    or those who don't use terminal shortcuts regularly.

OK, mainly because of the difference with the scrollback buffer which I
see is different. (Ctrl-l is a great one to know, it works in almost
everything, not just qemu, it's a basic ASCII control code going
back about 60 years)

Now to get to the magic line:

> >> +void hmp_clear(Monitor *mon, const QDict *qdict)
> >> +{
> >> +    monitor_printf(mon, "\x1b[3J\x1b[2J\x1b[H");

Firstly it would be great to comment this; as I read it,
this is:
   clear scrollback
   clear screen
   cursor back to top-left

But, this has a problem - for me on both mate-terminal and
terminator (but not konsole), this doesn't completely clear
the scrollback; it clears most of the scrollback, but leaves
about one page; my guess is what happens here is you clear
the scrollback, but then the current screen goes into it
after/when you clear it.

Looking at the output of the ncurses 'clear' command:

dg@dalek:~$ clear|xxd -g 1
00000000: 1b 5b 48 1b 5b 32 4a 1b 5b 33 4a                 .[H.[2J.[3J

it's got them in the opposite order, cursor, clear screen, clear scrollback
and that's fine in both mate-terminal/terminator & konsole.
(This is Fedora 44 with vte291-0.84.0-1.fc44.x86_64 being used by mate-terminal).
[I can't tell you if that's a bug in one or both of the terminals]

So please, flip the output around, and add a comment.

Thanks,

Dave
> >> +}
> >> +
> >>  void hmp_info_help(Monitor *mon, const QDict *qdict)
> >>  {
> >>      hmp_help_cmd(mon, "info");
> >> -- 
> >> 2.43.0
> >> 
> >-- 
> > -----Open up your eyes, open up your mind, open up your code -------   
> >/ Dr. David Alan Gilbert    |       Running GNU/Linux       | Happy  \ 
> >\        dave @ treblig.org |                               | In Hex /
> > \ _________________________|_____ http://www.treblig.org   |_______/
-- 
 -----Open up your eyes, open up your mind, open up your code -------   
/ Dr. David Alan Gilbert    |       Running GNU/Linux       | Happy  \ 
\        dave @ treblig.org |                               | In Hex /
 \ _________________________|_____ http://www.treblig.org   |_______/