Re: [Qemu-devel] [PATCH v2 1/1] virtio: serial: expose a 'guest_writable' callback for users

[Amit Shah <amit.shah@redhat.com>]

On (Thu) 09 Oct 2014 [14:04:53], Peter Maydell wrote:
> On 9 October 2014 13:17, Amit Shah <amit.shah@redhat.com> wrote:
> > On (Thu) 09 Oct 2014 [13:18:16], Markus Armbruster wrote:
> >> The code should work, but whether it makes sense is hard to judge for
> >> virtio noobs like me without a user of guest_writable.  The conditional
> >> guarding vsc->guest_writable(port) in particular.
> >
> > Right.  This was originally requested by the spice folks, and they
> > don't yet have a user implemented (waiting for the spice-char
> > implementation).  But Peter came up with a user; so I posted this w/o
> > the spice part of it.  But looks like Peter has lost the code for his
> > user, so this patch will have to wait ;-)
> 
> I have the QEMU code...
> 
> https://git.linaro.org/people/peter.maydell/qemu-arm.git/patch/33895359ddee3696bb24eac24cf8ee4cd697c72c
> 
> ...I just lost the bit of userspace code I was using to test it
> It's not very interesting as a use case though since it's
> just an echo-back-everything-you-say test backend (but it
> does demonstrate that there are basic things you can't do
> at all without some variation on this API).
> 
> What I would like to see in this patch is a comment giving
> much clearer definition of the semantics of the guest_writable
> call: for instance, is it always called when the guest is
> writable, or is it only guaranteed to be called if the
> QEMU backend has previously tried to do virtio_serial_write
> and got back a return code indicating an incomplete write?

Right now it's called always; if it's necessary to only call after an
incomplete / failed write, we just need to implement that (and also
add that state to the migration data).

I have no preference; just depends on the users of the API.


		Amit