Re: [Qemu-devel] [PATCH] usb: Remove legacy -usbdevice option

[Eric Blake]

On 01/04/2018 06:44 AM, Thomas Huth wrote:
> On 04.01.2018 13:33, Peter Maydell wrote:
>> On 4 January 2018 at 12:27, Thomas Huth <address@hidden> wrote:
>>> The option has been marked as deprecated since QEMU 2.10, and so far
>>> nobody complained that it is urgently required anymore. So let's now
>>> get rid of this legacy pile, to simplify the usb code quite a bit.
>>>
>>> Signed-off-by: Thomas Huth <address@hidden>
>>
>> The diffstat is nice, but can we retain the "please use
>> $NEWOPTION instead of $OLDOPTION" message for a bit?
>> I'm pretty sure there will be users out there who've
>> been happily ignoring deprecation notices, and I think
>> we'll reduce the amount of support traffic if they
>> get a new QEMU with a specific error message telling them
>> what they need to fix, rather than one which just prints
>> a generic "unknown option" message.
> 
> Sounds like a good idea at the first glance ... but at a second thought:
> Don't we confuse the management layers like libvirt this way, which
> might probe for the availability of this option by executing QEMU with
> this parameter?

At least for libvirt, probing for supported command line arguments is
preferable via QMP commands; if there is an easy way to make the
-usbdevice command line argument exist to emit the warning, but not show
up in the list of commands exposed over QMP, that is nicest (but I don't
know how that would interact with Markus' plans to make ALL command line
arguments introspectible, instead of our current ad hoc mix where some
are and others are not).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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