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

[Paolo Bonzini <pbonzini@redhat.com>]

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?

> One other example is the "-net nic,model=?" help text. It is inaccurate for a
> couple of machines - and if somebody tries to fix problems like this, you're
> often told something like "oh, it's the legacy -net option, simply forget about
> that" [2].

Nobody mentioned legacy in that thread...  Alex just said *he* would not
bother, but if you could come up with a better way to do it, it would
surely be accepted.

For example you could print all DEVICE_CATEGORY_NETWORK devices that
support device_add.

> And if you additionally ever had to deal with all that vlan code and duplicated
> option parsing stuff in the net/ code, then you certainly do not think anymore
> that this is just a little bit more than "syntactic sugar".

In fact there isn't much shared code in the is_netdev=0 and is_netdev=1
cases.  Perhaps you could just make a shared function with just

    if (net_client_init_fun[opts->type](opts, name, peer, errp) < 0) {
        /* FIXME drop when all init functions store an Error */
        if (errp && !*errp) {
            error_setg(errp, QERR_DEVICE_INIT_FAILED,
                       NetClientOptionsKind_lookup[opts->type]);
        }
        return -1;
    }


and inline all the rest of net_client_init1, net_visit, net_client_init
into two functions netdev_add and net_legacy_add.  Then -net handling
(including HMP) can be moved into a separate file which no one looks at.

> I'm fine if we keep the "-net" options for a couple of more versions of QEMU,
> but we should be prepared to be able to remove it quickly once it is getting into
> the way again too much. So we better start nagging the users about "-net" being
> deprecated now, than discovering later that we have to deal with this legacy
> stuff for longer than we would like to.

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. :)

Paolo