Re: [Qemu-devel] [PATCH] net: Inform the user about deprecated -net options

[Paolo Bonzini]

On 15/12/2015 18:15, Thomas Huth wrote:
> On 15/12/15 17:21, Paolo Bonzini wrote:
>> On 15/12/2015 17:01, Thomas Huth wrote:
>>> Some options work with "-net", some only work with "-netdev",
>>> and the ones that work with both often also behave slightly differently (see
>>> [1] for example).
>>
>> This example is about -net nic, which you're keeping.  What are the
>> options that differ between them for network backends?
> 
> The vlan option only exists for the "-net" backends.

Yup, vlans (implicit hubs) are the main difference between -net and
-netdev.  That's pretty much the only one, and it's not specific to
single backends.

> And I somehow
> thought that all the vhost related stuff would only work with the
> "-netdev", but I can not spot that in the code anymore, so I guess I
> simply got that wrong.

vhost probably doesn't start unless you use -netdev.  It's just ignored.
 But I may also be remembering wrong.

> Ok, maybe should have cited this one here instead:
> https://lists.gnu.org/archive/html/qemu-ppc/2013-11/msg00040.html
> 
> Markus said: "My advice would be to let -net nic rot in peace."

That would have meant not supporting "-net nic,model=ibmveth" to begin
with.  Too late, so a good solution would always be accepted.  We deal
with "legacy" stuff all the time, and sometime even improve it.

To some extent HMP is considered legacy for example, but no one in their
right minds would eliminate it.

>> For example you could print all DEVICE_CATEGORY_NETWORK devices that
>> support device_add.
> 
> I think that would not work since spapr-vlan is not hot-pluggable.

cannot_instantiate_with_device_add_yet which actually refers to -device,
not really device_add, so it would work.

The only issue would be that the default name is spapr-vlan rather than
ibmveth.  That would be not too bad as a backwards-incompatible change.

>> The thing is, people are still running QEMU from the command line.
>>
>> "-net nic -net bridge,br=virbr0" is still much less of a mouthful than
>> "-netdev bridge,br=virbr0,id=br -device rtl8139,netdev=br" if all I want
>> is something I can ssh into.
>>
>> It's easy to deprecate things.  It's hard to convince users that it's
>> worth, and you haven't convinced this user. :)
> 
> Ok, if you want to maintain that legacy stuff forever - fine.

I don't want to, but I think we have to.  It would be a good idea to get
rid of it, but unfortunately it's not a feasible idea IMHO.

> I thought it would be a good idea to slowly get rid off it, but honestly, if
> there's so much resistance ... I've also got other stuff to do, so
> simply forget about this.

I'm sorry.  It's just that _I_ would be a bit pissed off by it, even
though I type 500-characters QEMU command lines daily, therefore I think
end users would complain even more.  I would live with it, but for
regular users I don't think we would do them a great service.

It's the same as all the other shortcut options (-hda, -drive with
if!=none, -vga).  Many of them enjoy similar amounts of cruft, but they
cannot really go away. :(

Paolo