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Date: Tue, 14 May 2013 14:13:48 -0400
From: John Baboval <john.baboval@citrix.com>
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Subject: Re: [Qemu-devel] [PATCH v4] Add 'maxqdepth' as an option to tty
 character devices.
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To: Eric Blake <eblake@redhat.com>
Cc: "John V. Baboval" <john.baboval@virtualcomputer.com>, qemu-devel@nongnu.org

On 05/10/2013 11:28 PM, Eric Blake wrote:
> On 05/07/2013 04:39 PM, John Baboval wrote:
>> From: "John V. Baboval" <john.baboval@virtualcomputer.com>
>>
>> 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.