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>
Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
---
 chardev/char.c | 14 ++++++++++++++
 qapi/char.json | 22 ++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/chardev/char.c b/chardev/char.c
index b45d79cb9b57643827eb7479257fdda2cf6b0434..6e3ade98614c949be8041ec5905a490ff536dee9 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_resize(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..0a26c5eee6b71bc5de127a91b253cc69a9fe8ce6 100644
--- a/qapi/char.json
+++ b/qapi/char.json
@@ -874,6 +874,28 @@
 { 'command': 'chardev-send-break',
   'data': { 'id': 'str' } }
 
+##
+# @chardev-resize:
+#
+# Notifies a chardev about the current size of the terminal connected
+# to this chardev.
+#
+# @id: the chardev's ID, must exist
+# @cols: the number of columns
+# @rows: the number of rows
+#
+# Since: 10.2
+#
+# .. qmp-example::
+#
+#     -> { "execute": "chardev-resize", "arguments": { "id": "foo", "cols": 80, "rows": 24 } }
+#     <- { "return": {} }
+##
+{ 'command': 'chardev-resize',
+  'data': { 'id': 'str',
+            'cols': 'uint16',
+            'rows': 'uint16' } }
+
 ##
 # @VSERPORT_CHANGE:
 #

-- 
2.51.0

Cc: libvirt

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>
> Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
> ---
>  chardev/char.c | 14 ++++++++++++++
>  qapi/char.json | 22 ++++++++++++++++++++++
>  2 files changed, 36 insertions(+)
>
> diff --git a/chardev/char.c b/chardev/char.c
> index b45d79cb9b57643827eb7479257fdda2cf6b0434..6e3ade98614c949be8041ec5905a490ff536dee9 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_resize(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..0a26c5eee6b71bc5de127a91b253cc69a9fe8ce6 100644
> --- a/qapi/char.json
> +++ b/qapi/char.json
> @@ -874,6 +874,28 @@
>  { 'command': 'chardev-send-break',
>    'data': { 'id': 'str' } }
>  
> +##
> +# @chardev-resize:

This name doesn't tell me what is being resized.  PATCH 04 uses
"winsize", which is better.  The (losely) related SIGWINCH suggests
"window change" or "window size change".  Below, you use "terminal
size".

> +#
> +# Notifies a chardev about the current size of the terminal connected
> +# to this chardev.

Yes, but what is it good for?  Your commit message tells: "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."

> +#
> +# @id: the chardev's ID, must exist
> +# @cols: the number of columns
> +# @rows: the number of rows

Blank lines between the argument descriptions, bease.

What's the initial size?

Do we need a way to query the size?

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

On Fri, 2025-09-12 at 16:01 +0200, Markus Armbruster wrote:
> Cc: libvirt
> 
> 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>
> > Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
> > ---
> >  chardev/char.c | 14 ++++++++++++++
> >  qapi/char.json | 22 ++++++++++++++++++++++
> >  2 files changed, 36 insertions(+)
> > 
> > diff --git a/chardev/char.c b/chardev/char.c
> > index b45d79cb9b57643827eb7479257fdda2cf6b0434..6e3ade98614c949be8041ec5905a490ff536dee9 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_resize(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..0a26c5eee6b71bc5de127a91b253cc69a9fe8ce6 100644
> > --- a/qapi/char.json
> > +++ b/qapi/char.json
> > @@ -874,6 +874,28 @@
> >  { 'command': 'chardev-send-break',
> >    'data': { 'id': 'str' } }
> >  
> > +##
> > +# @chardev-resize:
> 
> This name doesn't tell me what is being resized.  PATCH 04 uses
> "winsize", which is better.  The (losely) related SIGWINCH suggests
> "window change" or "window size change".  Below, you use "terminal
> size".

How about chardev-console-resize? That would match the name of the
virtio event (VIRTIO_CONSOLE_RESIZE).

> > +#
> > +# Notifies a chardev about the current size of the terminal connected
> > +# to this chardev.
> 
> Yes, but what is it good for?  Your commit message tells: "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."

How about:

   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.

> > +#
> > +# @id: the chardev's ID, must exist
> > +# @cols: the number of columns
> > +# @rows: the number of rows
> 
> Blank lines between the argument descriptions, bease.
> 
> What's the initial size?

0x0

> Do we need a way to query the size?

I don't think it is necessary. What would be the usecase for that?

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

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

> On Fri, 2025-09-12 at 16:01 +0200, Markus Armbruster wrote:
>> Cc: libvirt
>> 
>> 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>
>> > Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
>> > ---
>> >  chardev/char.c | 14 ++++++++++++++
>> >  qapi/char.json | 22 ++++++++++++++++++++++
>> >  2 files changed, 36 insertions(+)
>> > 
>> > diff --git a/chardev/char.c b/chardev/char.c
>> > index b45d79cb9b57643827eb7479257fdda2cf6b0434..6e3ade98614c949be8041ec5905a490ff536dee9 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_resize(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..0a26c5eee6b71bc5de127a91b253cc69a9fe8ce6 100644
>> > --- a/qapi/char.json
>> > +++ b/qapi/char.json
>> > @@ -874,6 +874,28 @@
>> >  { 'command': 'chardev-send-break',
>> >    'data': { 'id': 'str' } }
>> >  
>> > +##
>> > +# @chardev-resize:
>> 
>> This name doesn't tell me what is being resized.  PATCH 04 uses
>> "winsize", which is better.  The (losely) related SIGWINCH suggests
>> "window change" or "window size change".  Below, you use "terminal
>> size".
>
> How about chardev-console-resize? That would match the name of the
> virtio event (VIRTIO_CONSOLE_RESIZE).

Not bad.  It could become slightly bad if we make devices other than
"consoles" make us of it.  Would that be possible?

>> > +#
>> > +# Notifies a chardev about the current size of the terminal connected
>> > +# to this chardev.
>> 
>> Yes, but what is it good for?  Your commit message tells: "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."
>
> How about:
>
>    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.

Works for me.

>> > +#
>> > +# @id: the chardev's ID, must exist
>> > +# @cols: the number of columns
>> > +# @rows: the number of rows
>> 
>> Blank lines between the argument descriptions, bease.
>> 
>> What's the initial size?
>
> 0x0

A clearly invalid size.  I guess it effectively means "unknown size".
Should we document that?

>> Do we need a way to query the size?
>
> I don't think it is necessary. What would be the usecase for that?

I don't know, but it's my standard question when I see an interface to
set something without an interface to get it.  Its purpose is to make us
think, not to make us at the get blindly.

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

On Mon, 2025-09-15 at 08:35 +0200, Markus Armbruster wrote:
> Filip Hejsek <filip.hejsek@gmail.com> writes:
> 
> > On Fri, 2025-09-12 at 16:01 +0200, Markus Armbruster wrote:
> > > Cc: libvirt
> > > 
> > > 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>
> > > > Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
> > > > ---
> > > >  chardev/char.c | 14 ++++++++++++++
> > > >  qapi/char.json | 22 ++++++++++++++++++++++
> > > >  2 files changed, 36 insertions(+)
> > > > 
> > > > diff --git a/chardev/char.c b/chardev/char.c
> > > > index b45d79cb9b57643827eb7479257fdda2cf6b0434..6e3ade98614c949be8041ec5905a490ff536dee9 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_resize(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..0a26c5eee6b71bc5de127a91b253cc69a9fe8ce6 100644
> > > > --- a/qapi/char.json
> > > > +++ b/qapi/char.json
> > > > @@ -874,6 +874,28 @@
> > > >  { 'command': 'chardev-send-break',
> > > >    'data': { 'id': 'str' } }
> > > >  
> > > > +##
> > > > +# @chardev-resize:
> > > 
> > > This name doesn't tell me what is being resized.  PATCH 04 uses
> > > "winsize", which is better.  The (losely) related SIGWINCH suggests
> > > "window change" or "window size change".  Below, you use "terminal
> > > size".
> > 
> > How about chardev-console-resize? That would match the name of the
> > virtio event (VIRTIO_CONSOLE_RESIZE).
> 
> Not bad.  It could become slightly bad if we make devices other than
> "consoles" make us of it.  Would that be possible?

I don't think the size has any meaning for devices that are not
connected to a console, although the code does not care whether it
actually is a console and simply has a size for every chardev.

I guess I could also rename it to chardev-window-resize
or chardev-set-window-size. Let me know if you prefer one of these.


> > > > +#
> > > > +# Notifies a chardev about the current size of the terminal connected
> > > > +# to this chardev.
> > > 
> > > Yes, but what is it good for?  Your commit message tells: "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."
> > 
> > How about:
> > 
> >    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.
> 
> Works for me.
> 
> > > > +#
> > > > +# @id: the chardev's ID, must exist
> > > > +# @cols: the number of columns
> > > > +# @rows: the number of rows
> > > 
> > > Blank lines between the argument descriptions, bease.
> > > 
> > > What's the initial size?
> > 
> > 0x0
> 
> A clearly invalid size.  I guess it effectively means "unknown size".
> Should we document that?

Probably. 0x0 is I think also the default size in the Linux kernel, but
I don't think the Linux kernel documents this. Another question is if
the 0x0 size should be propagated to the guest over virtio. I think it
should be, although the virtio spec says nothing about 0x0 size.

I'm not sure what is the right place to document this.

> > > Do we need a way to query the size?
> > 
> > I don't think it is necessary. What would be the usecase for that?
> 
> I don't know, but it's my standard question when I see an interface to
> set something without an interface to get it.  Its purpose is to make us
> think, not to make us at the get blindly.

I guess it might be useful for debugging. If the size is not propagated
correctly, one might query it to find out on which side the problem is.

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

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

> On Mon, 2025-09-15 at 08:35 +0200, Markus Armbruster wrote:
>> Filip Hejsek <filip.hejsek@gmail.com> writes:
>> 
>> > On Fri, 2025-09-12 at 16:01 +0200, Markus Armbruster wrote:
>> > > Cc: libvirt
>> > > 
>> > > 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>
>> > > > Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
>> > > > ---
>> > > >  chardev/char.c | 14 ++++++++++++++
>> > > >  qapi/char.json | 22 ++++++++++++++++++++++
>> > > >  2 files changed, 36 insertions(+)
>> > > > 
>> > > > diff --git a/chardev/char.c b/chardev/char.c
>> > > > index b45d79cb9b57643827eb7479257fdda2cf6b0434..6e3ade98614c949be8041ec5905a490ff536dee9 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_resize(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..0a26c5eee6b71bc5de127a91b253cc69a9fe8ce6 100644
>> > > > --- a/qapi/char.json
>> > > > +++ b/qapi/char.json
>> > > > @@ -874,6 +874,28 @@
>> > > >  { 'command': 'chardev-send-break',
>> > > >    'data': { 'id': 'str' } }
>> > > >  
>> > > > +##
>> > > > +# @chardev-resize:
>> > > 
>> > > This name doesn't tell me what is being resized.  PATCH 04 uses
>> > > "winsize", which is better.  The (losely) related SIGWINCH suggests
>> > > "window change" or "window size change".  Below, you use "terminal
>> > > size".
>> > 
>> > How about chardev-console-resize? That would match the name of the
>> > virtio event (VIRTIO_CONSOLE_RESIZE).
>> 
>> Not bad.  It could become slightly bad if we make devices other than
>> "consoles" make us of it.  Would that be possible?
>
> I don't think the size has any meaning for devices that are not
> connected to a console, although the code does not care whether it
> actually is a console and simply has a size for every chardev.

Double-checking: the command works for any ChardevBackendKind, doesn't
it?

> I guess I could also rename it to chardev-window-resize
> or chardev-set-window-size. Let me know if you prefer one of these.

I think I'd prefer "window" or "terminal".

"resize" and "set size" suggest that the command initiates a size
change.  Not true, it notifies of a size change.  Maybe
"chardev-window-size-changed", "chardev-terminal-size-changed",
"chardev-window-resized", or "chardev-terminal-resized".

>> > > > +#
>> > > > +# Notifies a chardev about the current size of the terminal connected
>> > > > +# to this chardev.
>> > > 
>> > > Yes, but what is it good for?  Your commit message tells: "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."
>> > 
>> > How about:
>> > 
>> >    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.
>> 
>> Works for me.
>> 
>> > > > +#
>> > > > +# @id: the chardev's ID, must exist
>> > > > +# @cols: the number of columns
>> > > > +# @rows: the number of rows
>> > > 
>> > > Blank lines between the argument descriptions, bease.
>> > > 
>> > > What's the initial size?
>> > 
>> > 0x0

Another question...  'vc' chardevs accept optional @rows, @cols (see
ChardevVC).  Is this the same size or something else?

>> A clearly invalid size.  I guess it effectively means "unknown size".
>> Should we document that?
>
> Probably. 0x0 is I think also the default size in the Linux kernel, but
> I don't think the Linux kernel documents this.

How does 0 x 0 behave compared to a valid size like 80 x 24?

>                                                Another question is if
> the 0x0 size should be propagated to the guest over virtio. I think it
> should be, although the virtio spec says nothing about 0x0 size.
>
> I'm not sure what is the right place to document this.

I think the QAPI schema doc comment is as good a place as any.

>> > > Do we need a way to query the size?
>> > 
>> > I don't think it is necessary. What would be the usecase for that?
>> 
>> I don't know, but it's my standard question when I see an interface to
>> set something without an interface to get it.  Its purpose is to make us
>> think, not to make us at the get blindly.
>
> I guess it might be useful for debugging. If the size is not propagated
> correctly, one might query it to find out on which side the problem is.

We have query-chardev.  It doesn't return much.

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

On Tue, 2025-09-16 at 15:07 +0200, Markus Armbruster wrote:
> Filip Hejsek <filip.hejsek@gmail.com> writes:
> 
> > On Mon, 2025-09-15 at 08:35 +0200, Markus Armbruster wrote:
> > > Filip Hejsek <filip.hejsek@gmail.com> writes:
> > > 
> > > > On Fri, 2025-09-12 at 16:01 +0200, Markus Armbruster wrote:
> > > > > Cc: libvirt
> > > > > 
> > > > > Filip Hejsek <filip.hejsek@gmail.com> writes:
> > > > > 
> > > > > > From: Szymon Lukasz <noh4hss@gmail.com>
> > > > > > 
> > > > > > [...]
> > > > > >  
> > > > > > +##
> > > > > > +# @chardev-resize:
> > > > > 
> > > > > This name doesn't tell me what is being resized.  PATCH 04 uses
> > > > > "winsize", which is better.  The (losely) related SIGWINCH suggests
> > > > > "window change" or "window size change".  Below, you use "terminal
> > > > > size".
> > > > 
> > > > How about chardev-console-resize? That would match the name of the
> > > > virtio event (VIRTIO_CONSOLE_RESIZE).
> > > 
> > > Not bad.  It could become slightly bad if we make devices other than
> > > "consoles" make us of it.  Would that be possible?
> > 
> > I don't think the size has any meaning for devices that are not
> > connected to a console, although the code does not care whether it
> > actually is a console and simply has a size for every chardev.
> 
> Double-checking: the command works for any ChardevBackendKind, doesn't
> it?

Yes. For some (e.g. stdio) it will clash with builtin resize detection,
but it can still be used (last update wins).

Maybe using the command should be prohibited for some device types?

> > I guess I could also rename it to chardev-window-resize
> > or chardev-set-window-size. Let me know if you prefer one of these.
> 
> I think I'd prefer "window" or "terminal".
> 
> "resize" and "set size" suggest that the command initiates a size
> change.  Not true, it notifies of a size change.  Maybe
> "chardev-window-size-changed", "chardev-terminal-size-changed",
> "chardev-window-resized", or "chardev-terminal-resized".

OK, then I'll use "chardev-window-size-changed".

> > > > > 
> > > > 
> [...]
> Another question...  'vc' chardevs accept optional @rows, @cols (see
> ChardevVC).  Is this the same size or something else?

Well, yes and no. @cols + @rows control the actual size of the console
screen buffer, while the chardev size is only used to inform the guest
about the size. @cols and @rows can also be unset, in which case the
size will be determined automatically from display and font size.

This patch series does not yet implement size propagation for the 'vc'
device. I have WIP patches for that, but there is something I'm not
sure how to do, so I will likely send an RFC first.

> > > A clearly invalid size.  I guess it effectively means "unknown size".
> > > Should we document that?
> > 
> > Probably. 0x0 is I think also the default size in the Linux kernel, but
> > I don't think the Linux kernel documents this.
> 
> How does 0 x 0 behave compared to a valid size like 80 x 24?

In these patches it is not treated specially (apart from being the
default). I think the Linux kernel doesn't treat it specially either.
Terminal programs generally interpret it as unknown size and use other
methods to obtain the size like environment variables, the terminfo
database, or defaulting to 80x24. Example:

   $ python -c 'import termios; termios.tcsetwinsize(0, (0,0))'
   $ tput cols
   80

> 
> [...]
> > > > > Do we need a way to query the size?
> > > > 
> > > > I don't think it is necessary. What would be the usecase for that?
> > > 
> > > I don't know, but it's my standard question when I see an interface to
> > > set something without an interface to get it.  Its purpose is to make us
> > > think, not to make us at the get blindly.
> > 
> > I guess it might be useful for debugging. If the size is not propagated
> > correctly, one might query it to find out on which side the problem is.
> 
> We have query-chardev.  It doesn't return much.

I'm not sure what you're implying. Shall I add the size there?
> > > > > 

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

> On Tue, 2025-09-16 at 15:07 +0200, Markus Armbruster wrote:
>> Filip Hejsek <filip.hejsek@gmail.com> writes:
>> 
>> > On Mon, 2025-09-15 at 08:35 +0200, Markus Armbruster wrote:
>> > > Filip Hejsek <filip.hejsek@gmail.com> writes:
>> > > 
>> > > > On Fri, 2025-09-12 at 16:01 +0200, Markus Armbruster wrote:
>> > > > > Cc: libvirt
>> > > > > 
>> > > > > Filip Hejsek <filip.hejsek@gmail.com> writes:
>> > > > > 
>> > > > > > From: Szymon Lukasz <noh4hss@gmail.com>
>> > > > > > 
>> > > > > > [...]
>> > > > > >  
>> > > > > > +##
>> > > > > > +# @chardev-resize:
>> > > > > 
>> > > > > This name doesn't tell me what is being resized.  PATCH 04 uses
>> > > > > "winsize", which is better.  The (losely) related SIGWINCH suggests
>> > > > > "window change" or "window size change".  Below, you use "terminal
>> > > > > size".
>> > > > 
>> > > > How about chardev-console-resize? That would match the name of the
>> > > > virtio event (VIRTIO_CONSOLE_RESIZE).
>> > > 
>> > > Not bad.  It could become slightly bad if we make devices other than
>> > > "consoles" make us of it.  Would that be possible?
>> > 
>> > I don't think the size has any meaning for devices that are not
>> > connected to a console, although the code does not care whether it
>> > actually is a console and simply has a size for every chardev.
>> 
>> Double-checking: the command works for any ChardevBackendKind, doesn't
>> it?
>
> Yes. For some (e.g. stdio) it will clash with builtin resize detection,
> but it can still be used (last update wins).
>
> Maybe using the command should be prohibited for some device types?

Depends on the command's intended use.

In general, failing a command is better than silently not doing what it
commands.  If the command is "tell the guest the window size changed",
and we can't, then failing the command is better than silently doing
nothing.

Howver, other considerations can trump this.  If we want to use this
command on any window size change without having to know the device
type, having it silently do nothing for device types that don't support
it can be more convenient.  Fine as long as the behavior is clearly
documented.

>> > I guess I could also rename it to chardev-window-resize
>> > or chardev-set-window-size. Let me know if you prefer one of these.
>> 
>> I think I'd prefer "window" or "terminal".
>> 
>> "resize" and "set size" suggest that the command initiates a size
>> change.  Not true, it notifies of a size change.  Maybe
>> "chardev-window-size-changed", "chardev-terminal-size-changed",
>> "chardev-window-resized", or "chardev-terminal-resized".
>
> OK, then I'll use "chardev-window-size-changed".
>
>> > > > > 
>> > > > 
>> [...]
>> Another question...  'vc' chardevs accept optional @rows, @cols (see
>> ChardevVC).  Is this the same size or something else?
>
> Well, yes and no. @cols + @rows control the actual size of the console
> screen buffer, while the chardev size is only used to inform the guest
> about the size. @cols and @rows can also be unset, in which case the
> size will be determined automatically from display and font size.

Thanks!

> This patch series does not yet implement size propagation for the 'vc'
> device. I have WIP patches for that, but there is something I'm not
> sure how to do, so I will likely send an RFC first.

Would it make sense to mention this gap in a commit message?

>> > > A clearly invalid size.  I guess it effectively means "unknown size".
>> > > Should we document that?
>> > 
>> > Probably. 0x0 is I think also the default size in the Linux kernel, but
>> > I don't think the Linux kernel documents this.
>> 
>> How does 0 x 0 behave compared to a valid size like 80 x 24?
>
> In these patches it is not treated specially (apart from being the
> default). I think the Linux kernel doesn't treat it specially either.
> Terminal programs generally interpret it as unknown size and use other
> methods to obtain the size like environment variables, the terminfo
> database, or defaulting to 80x24. Example:
>
>    $ python -c 'import termios; termios.tcsetwinsize(0, (0,0))'
>    $ tput cols
>    80

Do you think working this into the documentation would be useful?

>> [...]
>> > > > > Do we need a way to query the size?
>> > > > 
>> > > > I don't think it is necessary. What would be the usecase for that?
>> > > 
>> > > I don't know, but it's my standard question when I see an interface to
>> > > set something without an interface to get it.  Its purpose is to make us
>> > > think, not to make us at the get blindly.
>> > 
>> > I guess it might be useful for debugging. If the size is not propagated
>> > correctly, one might query it to find out on which side the problem is.
>> 
>> We have query-chardev.  It doesn't return much.
>
> I'm not sure what you're implying. Shall I add the size there?

If we could already query chardev configuration / state comprehensively,
then I'd ask you to make it cover your new state bits, too.

Since we don't, and there is no clear use case at this time, I'm not
asking you to do that.