On Mon, 2025-09-15 at 08:35 +0200, Markus Armbruster wrote:
> Filip Hejsek <[email protected]> writes:
>
> > On Fri, 2025-09-12 at 16:01 +0200, Markus Armbruster wrote:
> > > Cc: libvirt
> > >
> > > Filip Hejsek <[email protected]> writes:
> > >
> > > > From: Szymon Lukasz <[email protected]>
> > > >
> > > > 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 <[email protected]>
> > > > Suggested-by: Daniel P. Berrangé <[email protected]>
> > > > Signed-off-by: Filip Hejsek <[email protected]>
> > > > ---
> > > > 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:
> > > > #
