On Tue, Jan 20, 2026 at 11:16:51AM +0100, Filip Hejsek wrote: > On Tue, 2026-01-20 at 10:10 +0000, Daniel P. Berrangé wrote: > > On Tue, Jan 20, 2026 at 11:07:16AM +0100, Filip Hejsek wrote: > > > On Tue, 2026-01-20 at 09:54 +0000, Daniel P. Berrangé wrote: > > > > On Tue, Jan 20, 2026 at 10:50:04AM +0100, Filip Hejsek wrote: > > > > > On Mon, 2026-01-19 at 04:27 +0100, Filip Hejsek wrote: > > > > > > Implement the part of the virtio spec that allows to notify the > > > > > > virtio > > > > > > driver about terminal resizes. The virtio spec contains two methods > > > > > > to > > > > > > achieve that: > > > > > > > > > > > > For legacy drivers, we have only one port and we put the terminal > > > > > > size > > > > > > in the config space and inject the config changed interrupt. > > > > > > > > > > > > For multiport devices, we use the control virtqueue to send a packet > > > > > > containing the terminal size. Note that old versions of the Linux > > > > > > kernel > > > > > > used an incorrect order for the fields (rows then cols instead of > > > > > > cols > > > > > > then rows), until it was fixed by commit > > > > > > 5326ab737a47278dbd16ed3ee7380b26c7056ddd. > > > > > > > > > > > > As a result, when using a Linux kernel older than 6.15, the number > > > > > > of rows > > > > > > and columns will be swapped. > > > > > > > > > > > > Based on a patch originally written by Szymon Lukasz > > > > > > <[email protected]>, > > > > > > but partially rewritten to fix various corner cases. > > > > > > > > > > > > Signed-off-by: Szymon Lukasz <[email protected]> > > > > > > Signed-off-by: Filip Hejsek <[email protected]> > > > > > > --- > > > > > > hw/char/trace-events | 1 + > > > > > > hw/char/virtio-serial-bus.c | 76 > > > > > > +++++++++++++++++++++++++++++++++++++-- > > > > > > hw/core/machine.c | 4 ++- > > > > > > include/hw/virtio/virtio-serial.h | 5 +++ > > > > > > 4 files changed, 83 insertions(+), 3 deletions(-) > > > > > > > > > > > > [...] > > > > > > > > > > > > diff --git a/include/hw/virtio/virtio-serial.h > > > > > > b/include/hw/virtio/virtio-serial.h > > > > > > index 60641860bf..bda6d5312a 100644 > > > > > > --- a/include/hw/virtio/virtio-serial.h > > > > > > +++ b/include/hw/virtio/virtio-serial.h > > > > > > @@ -145,6 +145,9 @@ struct VirtIOSerialPort { > > > > > > bool host_connected; > > > > > > /* Do apps not want to receive data? */ > > > > > > bool throttled; > > > > > > + > > > > > > + /* Terminal size reported to the guest. Only used for > > > > > > consoles. */ > > > > > > + uint16_t cols, rows; > > > > > > }; > > > > > > > > > > I found a bug: after a migration, the guest is not informed about the > > > > > new console size. I see two ways to fix this: either add the cols and > > > > > rows fields to the migration stream, or always send the console size > > > > > to > > > > > the guest after migration, even if it might not have changed. Which do > > > > > you prefer? Modifying the migration stream is somewhat annoying, > > > > > because both versions will have to be supported, and also the device > > > > > still uses legacy save/load functions rather than VMState. > > > > > > > > On the backend side, I'd consider migration to be equivalent to closing > > > > and re-opening the backend character device. That should imply sending > > > > a resize event on migration completion. I'm surprised the chardev on > > > > the dst isn't already triggering that when it gets connected, but > > > > perhaps > > > > that is too early & getting lost ? > > > > > > The virtio device caches the size and doesn't send a resize message if > > > the size hasn't actually changed. > > > > If the size on the dest has not changed vs the size on the src, that's > > fine surely ? We only need to tell the guest a new size if the dst > > was different from the source after migration > > The current size is compared against previous size on the *dst*. We > don't know the size on the src, because it is not sent in the migration > stream.
Oh, I see what you mean. In that case we should probably use a .post_load hook to invalidate the dst cached size in some manner, so that the next update from the backend is forced to be sent to the guest. 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 :|
