* Re:Re: [PATCH] monitor: Add `clear` command
2026-04-18 17:23 ` Dr. David Alan Gilbert
@ 2026-04-19 7:43 ` Alano Song
2026-04-21 17:52 ` Dr. David Alan Gilbert
2026-04-19 8:43 ` Paolo Bonzini
2026-04-20 13:35 ` Alano Song
2 siblings, 1 reply; 7+ messages in thread
From: Alano Song @ 2026-04-19 7:43 UTC (permalink / raw)
To: Dr. David Alan Gilbert; +Cc: qemu-devel, pbonzini
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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
>
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.
>> ---
>> hmp-commands.hx | 14 ++++++++++++++
>> include/monitor/hmp.h | 1 +
>> monitor/hmp-cmds.c | 5 +++++
>> 3 files changed, 20 insertions(+)
>>
>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>> index 5cc4788f12..95f9166732 100644
>> --- a/hmp-commands.hx
>> +++ b/hmp-commands.hx
>> @@ -20,6 +20,20 @@ SRST
>> Show the help for all commands or just for command *cmd*.
>> ERST
>>
>> + {
>> + .name = "clear",
>> + .args_type = "",
>> + .params = "",
>> + .help = "clear the monitor screen",
>> + .cmd = hmp_clear,
>> + .flags = "p",
>> + },
>> +
>> +SRST
>> +``clear``
>> + Clear the monitor screen.
>> +ERST
>> +
>> {
>> .name = "commit",
>> .args_type = "device:B",
>> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
>> index e222bea60c..9b66458d21 100644
>> --- a/include/monitor/hmp.h
>> +++ b/include/monitor/hmp.h
>> @@ -165,6 +165,7 @@ void hmp_trace_event(Monitor *mon, const QDict *qdict);
>> void hmp_trace_file(Monitor *mon, const QDict *qdict);
>> void hmp_info_trace_events(Monitor *mon, const QDict *qdict);
>> void hmp_help(Monitor *mon, const QDict *qdict);
>> +void hmp_clear(Monitor *mon, const QDict *qdict);
>> void hmp_info_help(Monitor *mon, const QDict *qdict);
>> void hmp_info_sync_profile(Monitor *mon, const QDict *qdict);
>> void hmp_info_history(Monitor *mon, const QDict *qdict);
>> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
>> index bc26b39d70..3e9485478e 100644
>> --- a/monitor/hmp-cmds.c
>> +++ b/monitor/hmp-cmds.c
>> @@ -218,6 +218,11 @@ void hmp_help(Monitor *mon, const QDict *qdict)
>> hmp_help_cmd(mon, qdict_get_try_str(qdict, "name"));
>> }
>>
>> +void hmp_clear(Monitor *mon, const QDict *qdict)
>> +{
>> + monitor_printf(mon, "\x1b[3J\x1b[2J\x1b[H");
>> +}
>> +
>> 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 |_______/
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^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] monitor: Add `clear` command
2026-04-19 7:43 ` Alano Song
@ 2026-04-21 17:52 ` Dr. David Alan Gilbert
2026-04-22 13:44 ` Alano Song
0 siblings, 1 reply; 7+ messages in thread
From: Dr. David Alan Gilbert @ 2026-04-21 17:52 UTC (permalink / raw)
To: Alano Song; +Cc: qemu-devel, pbonzini
* 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 |_______/
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] monitor: Add `clear` command
2026-04-21 17:52 ` Dr. David Alan Gilbert
@ 2026-04-22 13:44 ` Alano Song
0 siblings, 0 replies; 7+ messages in thread
From: Alano Song @ 2026-04-22 13:44 UTC (permalink / raw)
To: Dr. David Alan Gilbert; +Cc: qemu-devel, pbonzini
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At 2026-04-22 01:52:54, "Dr. David Alan Gilbert" <dave@treblig.org> wrote:
>* 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)
>
Hi, Dr.Gilbert,
Thanks for sharing that, got it :)
>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
>
You are right, the command order on my ubuntu24.04 is the same with you:
alano@alano:~/code$ clear | xxd -g 1
00000000: 1b 5b 48 1b 5b 32 4a 1b 5b 33 4a .[H.[2J.[3J
So I will correct the command order sent in patch :)
>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
I will add comment in code and help info in v2 patch.
Best Regards,
Alano.
>> >> +}
>> >> +
>> >> 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 |_______/
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] monitor: Add `clear` command
2026-04-18 17:23 ` Dr. David Alan Gilbert
2026-04-19 7:43 ` Alano Song
@ 2026-04-19 8:43 ` Paolo Bonzini
2026-04-20 13:35 ` Alano Song
2 siblings, 0 replies; 7+ messages in thread
From: Paolo Bonzini @ 2026-04-19 8:43 UTC (permalink / raw)
To: Dr. David Alan Gilbert, AlanoSong; +Cc: qemu-devel
On 4/18/26 19:23, Dr. David Alan Gilbert 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?
Yeah, we should add support for Ctrl-L to the non-terminal backends
independent of this. However, backends such as socket do not use
readline so they also don't support it right now.
Paolo
> Dave
>
>> ---
>> hmp-commands.hx | 14 ++++++++++++++
>> include/monitor/hmp.h | 1 +
>> monitor/hmp-cmds.c | 5 +++++
>> 3 files changed, 20 insertions(+)
>>
>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>> index 5cc4788f12..95f9166732 100644
>> --- a/hmp-commands.hx
>> +++ b/hmp-commands.hx
>> @@ -20,6 +20,20 @@ SRST
>> Show the help for all commands or just for command *cmd*.
>> ERST
>>
>> + {
>> + .name = "clear",
>> + .args_type = "",
>> + .params = "",
>> + .help = "clear the monitor screen",
>> + .cmd = hmp_clear,
>> + .flags = "p",
>> + },
>> +
>> +SRST
>> +``clear``
>> + Clear the monitor screen.
>> +ERST
>> +
>> {
>> .name = "commit",
>> .args_type = "device:B",
>> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
>> index e222bea60c..9b66458d21 100644
>> --- a/include/monitor/hmp.h
>> +++ b/include/monitor/hmp.h
>> @@ -165,6 +165,7 @@ void hmp_trace_event(Monitor *mon, const QDict *qdict);
>> void hmp_trace_file(Monitor *mon, const QDict *qdict);
>> void hmp_info_trace_events(Monitor *mon, const QDict *qdict);
>> void hmp_help(Monitor *mon, const QDict *qdict);
>> +void hmp_clear(Monitor *mon, const QDict *qdict);
>> void hmp_info_help(Monitor *mon, const QDict *qdict);
>> void hmp_info_sync_profile(Monitor *mon, const QDict *qdict);
>> void hmp_info_history(Monitor *mon, const QDict *qdict);
>> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
>> index bc26b39d70..3e9485478e 100644
>> --- a/monitor/hmp-cmds.c
>> +++ b/monitor/hmp-cmds.c
>> @@ -218,6 +218,11 @@ void hmp_help(Monitor *mon, const QDict *qdict)
>> hmp_help_cmd(mon, qdict_get_try_str(qdict, "name"));
>> }
>>
>> +void hmp_clear(Monitor *mon, const QDict *qdict)
>> +{
>> + monitor_printf(mon, "\x1b[3J\x1b[2J\x1b[H");
>> +}
>> +
>> void hmp_info_help(Monitor *mon, const QDict *qdict)
>> {
>> hmp_help_cmd(mon, "info");
>> --
>> 2.43.0
>>
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH] monitor: Add `clear` command
2026-04-18 17:23 ` Dr. David Alan Gilbert
2026-04-19 7:43 ` Alano Song
2026-04-19 8:43 ` Paolo Bonzini
@ 2026-04-20 13:35 ` Alano Song
2 siblings, 0 replies; 7+ messages in thread
From: Alano Song @ 2026-04-20 13:35 UTC (permalink / raw)
To: Dr. David Alan Gilbert; +Cc: qemu-devel, pbonzini
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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
>
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.
Best Regards,
Alano.
// Re-send, it seems that the previous reply email is not visible in the mail list.
>> ---
>> hmp-commands.hx | 14 ++++++++++++++
>> include/monitor/hmp.h | 1 +
>> monitor/hmp-cmds.c | 5 +++++
>> 3 files changed, 20 insertions(+)
>>
>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>> index 5cc4788f12..95f9166732 100644
>> --- a/hmp-commands.hx
>> +++ b/hmp-commands.hx
>> @@ -20,6 +20,20 @@ SRST
>> Show the help for all commands or just for command *cmd*.
>> ERST
>>
>> + {
>> + .name = "clear",
>> + .args_type = "",
>> + .params = "",
>> + .help = "clear the monitor screen",
>> + .cmd = hmp_clear,
>> + .flags = "p",
>> + },
>> +
>> +SRST
>> +``clear``
>> + Clear the monitor screen.
>> +ERST
>> +
>> {
>> .name = "commit",
>> .args_type = "device:B",
>> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
>> index e222bea60c..9b66458d21 100644
>> --- a/include/monitor/hmp.h
>> +++ b/include/monitor/hmp.h
>> @@ -165,6 +165,7 @@ void hmp_trace_event(Monitor *mon, const QDict *qdict);
>> void hmp_trace_file(Monitor *mon, const QDict *qdict);
>> void hmp_info_trace_events(Monitor *mon, const QDict *qdict);
>> void hmp_help(Monitor *mon, const QDict *qdict);
>> +void hmp_clear(Monitor *mon, const QDict *qdict);
>> void hmp_info_help(Monitor *mon, const QDict *qdict);
>> void hmp_info_sync_profile(Monitor *mon, const QDict *qdict);
>> void hmp_info_history(Monitor *mon, const QDict *qdict);
>> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
>> index bc26b39d70..3e9485478e 100644
>> --- a/monitor/hmp-cmds.c
>> +++ b/monitor/hmp-cmds.c
>> @@ -218,6 +218,11 @@ void hmp_help(Monitor *mon, const QDict *qdict)
>> hmp_help_cmd(mon, qdict_get_try_str(qdict, "name"));
>> }
>>
>> +void hmp_clear(Monitor *mon, const QDict *qdict)
>> +{
>> + monitor_printf(mon, "\x1b[3J\x1b[2J\x1b[H");
>> +}
>> +
>> 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 |_______/
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^ permalink raw reply [flat|nested] 7+ messages in thread