From: Szymon Lukasz <noh4hss@gmail.com>

The managment software can use this command to notify QEMU about the
size of the terminal connected to a chardev, QEMU can then forward this
information to the guest if the chardev is connected to a virtio console
device.

Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
[Filip: rename command, change documentation]
Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
---
 chardev/char.c | 14 ++++++++++++++
 qapi/char.json | 30 ++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/chardev/char.c b/chardev/char.c
index b45d79cb9b57643827eb7479257fdda2cf6b0434..f3aad545afe3d325aac388015b3d5517c2e48f0d 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -1269,6 +1269,20 @@ bool qmp_add_client_char(int fd, bool has_skipauth, bool skipauth,
     return true;
 }
 
+void qmp_chardev_window_size_changed(const char *id, uint16_t cols,
+                                     uint16_t rows, Error **errp)
+{
+    Chardev *chr;
+
+    chr = qemu_chr_find(id);
+    if (chr == NULL) {
+        error_setg(errp, "Chardev '%s' not found", id);
+        return;
+    }
+
+    qemu_chr_resize(chr, cols, rows);
+}
+
 /*
  * Add a timeout callback for the chardev (in milliseconds), return
  * the GSource object created. Please use this to add timeout hook for
diff --git a/qapi/char.json b/qapi/char.json
index f0a53f742c8bee24c377551803a864fd36ac78cf..93b0d239276077d808af2e5479d539728377a99f 100644
--- a/qapi/char.json
+++ b/qapi/char.json
@@ -874,6 +874,36 @@
 { 'command': 'chardev-send-break',
   'data': { 'id': 'str' } }
 
+##
+# @chardev-window-size-changed:
+#
+# Notifies a chardev about the current size of the terminal connected
+# to this chardev. The information will be forwarded to the guest if
+# the chardev is connected to a virtio console device.
+#
+# The initial size is 0x0, which should be interpreted as an unknown size.
+#
+# Some backends detect the terminal size automatically, in which case
+# the size may unpredictably revert to the detected one at any time.
+#
+# @id: the chardev's ID, must exist
+#
+# @cols: the number of columns
+#
+# @rows: the number of rows
+#
+# Since: 10.2
+#
+# .. qmp-example::
+#
+#     -> { "execute": "chardev-window-size-changed", "arguments": { "id": "foo", "cols": 80, "rows": 24 } }
+#     <- { "return": {} }
+##
+{ 'command': 'chardev-window-size-changed',
+  'data': { 'id': 'str',
+            'cols': 'uint16',
+            'rows': 'uint16' } }
+
 ##
 # @VSERPORT_CHANGE:
 #

-- 
2.51.0

Filip Hejsek wrote on Sun, Sep 21, 2025 at 01:45:37AM +0200:
> +##
> +# @chardev-window-size-changed:
> +#
> +# Notifies a chardev about the current size of the terminal connected
> +# to this chardev. The information will be forwarded to the guest if
> +# the chardev is connected to a virtio console device.
> +#
> +# The initial size is 0x0, which should be interpreted as an unknown size.

Actually coming back to this: what does that "initial size" mean?

If there had been a qmp command to get the current size I'd understand,
but this is set-only as far as I can see, so there is no initial size?

(not that it matters)

Thanks,
-- 
Dominique Martinet | Asmadeus

Filip Hejsek wrote on Sun, Sep 21, 2025 at 01:45:37AM +0200:
> From: Szymon Lukasz <noh4hss@gmail.com>
> 
> The managment software can use this command to notify QEMU about the
> size of the terminal connected to a chardev, QEMU can then forward this
> information to the guest if the chardev is connected to a virtio console
> device.
> 
> Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
> Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
> [Filip: rename command, change documentation]
> Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>

Reviewed-by: Dominique Martinet <dominique.martinet@codewreck.org>
Tested-by: Dominique Martinet <dominique.martinet@codewreck.org>

(checked with stty in guest after running the command)

-- 
Dominique Martinet | Asmadeus

On Sun, Sep 21, 2025 at 01:45:37AM +0200, Filip Hejsek wrote:
> From: Szymon Lukasz <noh4hss@gmail.com>
> 
> The managment software can use this command to notify QEMU about the
> size of the terminal connected to a chardev, QEMU can then forward this
> information to the guest if the chardev is connected to a virtio console
> device.
> 
> Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
> Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
> [Filip: rename command, change documentation]
> Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
> ---
>  chardev/char.c | 14 ++++++++++++++
>  qapi/char.json | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|

Filip Hejsek <filip.hejsek@gmail.com> writes:

> From: Szymon Lukasz <noh4hss@gmail.com>
>
> The managment software can use this command to notify QEMU about the
> size of the terminal connected to a chardev, QEMU can then forward this
> information to the guest if the chardev is connected to a virtio console
> device.
>
> Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
> Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
> [Filip: rename command, change documentation]
> Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
> ---
>  chardev/char.c | 14 ++++++++++++++
>  qapi/char.json | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+)
>
> diff --git a/chardev/char.c b/chardev/char.c
> index b45d79cb9b57643827eb7479257fdda2cf6b0434..f3aad545afe3d325aac388015b3d5517c2e48f0d 100644
> --- a/chardev/char.c
> +++ b/chardev/char.c
> @@ -1269,6 +1269,20 @@ bool qmp_add_client_char(int fd, bool has_skipauth, bool skipauth,
>      return true;
>  }
>  
> +void qmp_chardev_window_size_changed(const char *id, uint16_t cols,
> +                                     uint16_t rows, Error **errp)
> +{
> +    Chardev *chr;
> +
> +    chr = qemu_chr_find(id);
> +    if (chr == NULL) {
> +        error_setg(errp, "Chardev '%s' not found", id);
> +        return;
> +    }
> +
> +    qemu_chr_resize(chr, cols, rows);
> +}
> +
>  /*
>   * Add a timeout callback for the chardev (in milliseconds), return
>   * the GSource object created. Please use this to add timeout hook for
> diff --git a/qapi/char.json b/qapi/char.json
> index f0a53f742c8bee24c377551803a864fd36ac78cf..93b0d239276077d808af2e5479d539728377a99f 100644
> --- a/qapi/char.json
> +++ b/qapi/char.json
> @@ -874,6 +874,36 @@
>  { 'command': 'chardev-send-break',
>    'data': { 'id': 'str' } }
>  
> +##
> +# @chardev-window-size-changed:
> +#
> +# Notifies a chardev about the current size of the terminal connected
> +# to this chardev. The information will be forwarded to the guest if
> +# the chardev is connected to a virtio console device.
> +#
> +# The initial size is 0x0, which should be interpreted as an unknown size.
> +#
> +# Some backends detect the terminal size automatically, in which case
> +# the size may unpredictably revert to the detected one at any time.

Nicely done now!

docs/devel/qapi-code-gen.rst:

    For legibility, wrap text paragraphs so every line is at most 70
    characters long.

    Separate sentences with two spaces.

> +#
> +# @id: the chardev's ID, must exist

Let's drop ", must exist" for consistency with ID descriptions
elsewhere.

> +#
> +# @cols: the number of columns
> +#
> +# @rows: the number of rows
> +#
> +# Since: 10.2
> +#
> +# .. qmp-example::
> +#
> +#     -> { "execute": "chardev-window-size-changed", "arguments": { "id": "foo", "cols": 80, "rows": 24 } }
> +#     <- { "return": {} }
> +##
> +{ 'command': 'chardev-window-size-changed',
> +  'data': { 'id': 'str',
> +            'cols': 'uint16',
> +            'rows': 'uint16' } }
> +
>  ##
>  # @VSERPORT_CHANGE:
>  #

Acked-by: Markus Armbruster <armbru@redhat.com>

On Mon, 2025-09-22 at 08:45 +0200, Markus Armbruster wrote:
> Filip Hejsek <filip.hejsek@gmail.com> writes:
> 
> > From: Szymon Lukasz <noh4hss@gmail.com>
> > 
> > The managment software can use this command to notify QEMU about the
> > size of the terminal connected to a chardev, QEMU can then forward this
> > information to the guest if the chardev is connected to a virtio console
> > device.
> > 
> > Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
> > Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
> > [Filip: rename command, change documentation]
> > Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
> > ---
> >  chardev/char.c | 14 ++++++++++++++
> >  qapi/char.json | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 44 insertions(+)
> > 
> > diff --git a/chardev/char.c b/chardev/char.c
> > index b45d79cb9b57643827eb7479257fdda2cf6b0434..f3aad545afe3d325aac388015b3d5517c2e48f0d 100644
> > --- a/chardev/char.c
> > +++ b/chardev/char.c
> > @@ -1269,6 +1269,20 @@ bool qmp_add_client_char(int fd, bool has_skipauth, bool skipauth,
> >      return true;
> >  }
> >  
> > +void qmp_chardev_window_size_changed(const char *id, uint16_t cols,
> > +                                     uint16_t rows, Error **errp)
> > +{
> > +    Chardev *chr;
> > +
> > +    chr = qemu_chr_find(id);
> > +    if (chr == NULL) {
> > +        error_setg(errp, "Chardev '%s' not found", id);
> > +        return;
> > +    }
> > +
> > +    qemu_chr_resize(chr, cols, rows);
> > +}
> > +
> >  /*
> >   * Add a timeout callback for the chardev (in milliseconds), return
> >   * the GSource object created. Please use this to add timeout hook for
> > diff --git a/qapi/char.json b/qapi/char.json
> > index f0a53f742c8bee24c377551803a864fd36ac78cf..93b0d239276077d808af2e5479d539728377a99f 100644
> > --- a/qapi/char.json
> > +++ b/qapi/char.json
> > @@ -874,6 +874,36 @@
> >  { 'command': 'chardev-send-break',
> >    'data': { 'id': 'str' } }
> >  
> > +##
> > +# @chardev-window-size-changed:
> > +#
> > +# Notifies a chardev about the current size of the terminal connected
> > +# to this chardev. The information will be forwarded to the guest if
> > +# the chardev is connected to a virtio console device.
> > +#
> > +# The initial size is 0x0, which should be interpreted as an unknown size.
> > +#
> > +# Some backends detect the terminal size automatically, in which case
> > +# the size may unpredictably revert to the detected one at any time.
> 
> Nicely done now!
> 
> docs/devel/qapi-code-gen.rst:
> 
>     For legibility, wrap text paragraphs so every line is at most 70
>     characters long.
> 
>     Separate sentences with two spaces.
> 
> > +#
> > +# @id: the chardev's ID, must exist
> 
> Let's drop ", must exist" for consistency with ID descriptions
> elsewhere.

All chardev @id parameters in qapi/char.json have ", must exist"
(although you're right that nothing else has it).

> > +#
> > +# @cols: the number of columns
> > +#
> > +# @rows: the number of rows
> > +#
> > +# Since: 10.2
> > +#
> > +# .. qmp-example::
> > +#
> > +#     -> { "execute": "chardev-window-size-changed", "arguments": { "id": "foo", "cols": 80, "rows": 24 } }
> > +#     <- { "return": {} }
> > +##
> > +{ 'command': 'chardev-window-size-changed',
> > +  'data': { 'id': 'str',
> > +            'cols': 'uint16',
> > +            'rows': 'uint16' } }
> > +
> >  ##
> >  # @VSERPORT_CHANGE:
> >  #
> 
> Acked-by: Markus Armbruster <armbru@redhat.com>

Filip Hejsek <filip.hejsek@gmail.com> writes:

> On Mon, 2025-09-22 at 08:45 +0200, Markus Armbruster wrote:
>> Filip Hejsek <filip.hejsek@gmail.com> writes:
>> 
>> > From: Szymon Lukasz <noh4hss@gmail.com>
>> > 
>> > The managment software can use this command to notify QEMU about the
>> > size of the terminal connected to a chardev, QEMU can then forward this
>> > information to the guest if the chardev is connected to a virtio console
>> > device.
>> > 
>> > Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
>> > Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
>> > [Filip: rename command, change documentation]
>> > Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>

[...]

>> > diff --git a/qapi/char.json b/qapi/char.json
>> > index f0a53f742c8bee24c377551803a864fd36ac78cf..93b0d239276077d808af2e5479d539728377a99f 100644
>> > --- a/qapi/char.json
>> > +++ b/qapi/char.json
>> > @@ -874,6 +874,36 @@
>> >  { 'command': 'chardev-send-break',
>> >    'data': { 'id': 'str' } }
>> >  
>> > +##
>> > +# @chardev-window-size-changed:
>> > +#
>> > +# Notifies a chardev about the current size of the terminal connected
>> > +# to this chardev. The information will be forwarded to the guest if
>> > +# the chardev is connected to a virtio console device.
>> > +#
>> > +# The initial size is 0x0, which should be interpreted as an unknown size.
>> > +#
>> > +# Some backends detect the terminal size automatically, in which case
>> > +# the size may unpredictably revert to the detected one at any time.
>> 
>> Nicely done now!
>> 
>> docs/devel/qapi-code-gen.rst:
>> 
>>     For legibility, wrap text paragraphs so every line is at most 70
>>     characters long.
>> 
>>     Separate sentences with two spaces.
>> 
>> > +#
>> > +# @id: the chardev's ID, must exist
>> 
>> Let's drop ", must exist" for consistency with ID descriptions
>> elsewhere.
>
> All chardev @id parameters in qapi/char.json have ", must exist"
> (although you're right that nothing else has it).

Right.  Feel free to stay locally consistent then.

[...]