On Thu, Jan 9, 2025 at 7:07 PM Daniel P. Berrangé <berra...@redhat.com> wrote: > > On Thu, Jan 09, 2025 at 01:56:40PM +0100, Roman Penyaev wrote: > > Hi, > > > > On Tue, Jan 7, 2025 at 3:57 PM Marc-André Lureau > > <marcandre.lur...@redhat.com> wrote: > > > Whether we talk about multiplexing front-end or back-end, the issues > > > are similar. In general, mixing input will create issues. Teeing > > > output is less problematic, except to handle the buffering... > > > > I understand your concerns. What exact issues do you have in mind? > > Are these issues related to the input buffer handling, so technical issues? > > Or issues with usability? > > While the design / impl technically allows for concurrent input to be > sent to the frontend, from multiple backends, in practice I don't think > we need to be particularly concerned about it. > > I don't see this as being a way for multiple different users to interact > concurrently. Rather I'd see 1 user of the VM just deciding to switch > from one backend to the other on the fly. IOW, although technically > possible, the user will only be leveraging one at a time to send input. > > We very definitely do need all backends to receive output from the guest > concurrently too, as you'd want the historical output context to be > visible on whatever backend you choose to use at any given point in time. > > If a user decides to be crazy and send input from multiple backends > concurrently, then they get to keep the mess. > > > > > Do you think we need to artificially introduce multiplexing logic to be > > > > fully > > > > compliant with multiplexer naming? It's not hard to do, repeating > > > > `mux_proc_byte()` from `mux-fe`. In my use-case, I'll still need to > > > > disable > > > > multiplexing in favor of 'mixing', for example with the 'mixer=on' > > > > option, > > > > i.e. '-chardev mux-be,mixer=on,...`. Or do you think it should be some > > > > completely different beast, something like mixer chardev? > > > > > > I think it would be saner to have the muxer be selectors: only work > > > with one selected be or fe. Otherwise, we can run into various issues. > > > > In multiplexing (not mixing) for the use-case that I am describing, there > > is one > > serious drawback: as soon as you switch the "focus" to another input device > > (for example from vnc to socket chardev), you will not be able to s]witch > > back > > from the same input console - the input now works on another device. This > > looks > > strange and does not add convenience to the final user. Perhaps, for a case > > other than console, this would be reasonable, but for console input - > > I would like > > to keep the mixer option: the front-end receives input from both back-ends. > > Agreed, I think this is desirable. If you did the exclusive access mode, > it'd complicate things as you now need a way to switch between active > backends, while also reducing the usefulness of it. > > The main thing I'm not a fan of here is the naming 'mux-fe', as I think we > should have something distinct from current 'mux', to reduce confusion > when we're talking about it.
The idea to have mux-fe and mux-be (current implementation) was born to distinguish what exactly we multiplex: front-ends or back-ends. As Mark-Andre rightly noted, input from back-end devices is not multiplexed, but rather mixed. > > How about 'overlay' or 'replicator' ? Overlay for me has a strong association with the filesystem concept. This would work for me if combined back-end inputs function by layering one on top of another, with potentially higher-priority inputs overriding lower-priority ones. It implies a hierarchical or layered merging approach. Not quite well describes a simple mixing strategy. Replicator - this can be a good name from front-end device point of view: suggests a mechanism for distributing the same input (front-end) to different destinations (back-ends). Two more: what about 'aggregator' or even 'hub' ? Also 'mixer'? So we have '-chardev mux' and '-chardev mix' (try not to get confused :) -- Roman
