On Mon, 2020-07-20 at 19:36 +0100, Daniel P. Berrangé wrote: > On Mon, Jul 20, 2020 at 08:20:12PM +0200, Andrea Bolognani wrote: > > We could special-case binaries called 'virt-nc' and use our internal > > syntax for those. Having two separate URI parameters to control the > > same knob sounds like trouble, especially since you can mix and > > match: if you try to connect to > > > > qemu+ssh://host/system?proxy=virt-nc&netcat=my-cool-nc > > > > for example, what happens? As far as I can tell virt-nc will be used, > > but it's certainly not as obvious as it would be if everything was > > controlled by a single URI parameter. > > No, I really don't want to do magic based on the name of the binary. > That is a recipe for long term pain. It never turns out well when we > try to overload two distinct concepts onto a single tunable. > > That URL you illustrate should be reported as an error since it > is using mutually exclusive args. Adding validation sounds good. We should also cross-reference the two parameters in the documentation, to make sure users changing one of them is aware of the other existing as well. > > Actually, and I might be very well missing something because I looked > > at the code rather quickly, from what I can tell the default value > > for proxy will cause libvirt to always prefer virt-nc when available, > > which means that the URI > > > > qemu+ssh://host/system?netcat=my-cool-nc > > > > will suddenly stop using my-cool-nc and start using virt-nc after > > libvirt has been upgraded - a breaking change. > > It will only stop using my-cool-nc if you have upgraded the remote > host to have virt-nc installed, and your local host also has the > libvirt supporting virt-nc. I'd consider that desirable, as netcat > is redundant once both sides are upgraded. If the user is explicitly asking for a specific netcat binary to be used, then we need to comply with that request, even if we think that virt-nc would be better. Doing otherwise has the potential to break the user's setup. Basically, when the netcat parameter is specified we should behave as if proxy=netcat had been specified as well. -- Andrea Bolognani / Red Hat / Virtualization
