Re: [Qemu-devel] [PATCH v4] Add 'maxqdepth' as an option to tty character devices.

[John Baboval]

On 05/10/2013 11:28 PM, Eric Blake wrote:
> On 05/07/2013 04:39 PM, John Baboval wrote:
> > From: "John V. Baboval" <address@hidden>
> >
> > This parameter will cause writes to tty backed chardevs to return
> > -EAGAIN if the backing tty has buffered more than the specified
> > number of characters. When data is sent, the TIOCOUTQ ioctl is invoked
> > to determine the current TTY output buffer depth.
> >
> > +++ b/qapi-schema.json
> > @@ -3182,11 +3182,14 @@
> >   #
> >   # @device: The name of the special file for the device,
> >   #          i.e. /dev/ttyS0 on Unix or COM1: on Windows
> > -# @type: What kind of device this is.
> > +#
> > +# @maxqdepth: #optional The maximum depth of the underlying tty
> > +#             output queue (Unix) (Since 1.6)
> >   #
> >   # Since: 1.4
> >   ##
> > -{ 'type': 'ChardevHostdev', 'data': { 'device' : 'str' } }
> > +{ 'type': 'ChardevHostdev', 'data': { 'device'    : 'str',
> > +                                      '*maxqdepth' : 'int' } }
> >   
> Thanks; this interface change looks better (I'd still like to see
> someone working on introspection, but it doesn't have to be you).  I'll
> still leave the implementation details to others more qualified for that
> part of the review.  In particular, since you are claiming this optional
> attribute is Linux-only, that means we'd need introspection to know
> whether a given qemu build supports the field (compiled on Linux) or not
> (compiled on mingw), not just whether the qemu is new enough (1.6) or
> older (1.4).
I believe (though I haven't tested on Windows) that the option at least 
does no harm there. You can still set it - It's just a no-op.