On Wed 29 Aug 2018 02:59:01 PM CEST, Max Reitz wrote: >>> Specifically, that means when you don't specify @backing, the default >>> chain will be opened and may replace the current one. >> >> At the moment "backing" is the only child option that can be omitted, >> all others must be specified. So if you leave "backing" out on reopen() >> we have the following possibilities: >> >> a) We open the default backing file from disk. I don't think we want >> to open a new image on reopen(). Plus, what happens if the current >> backing image is the default one? Do we need to detect that? And >> what if it's the default image but has non-default options? The >> whole thing looks like a can of worms. > > True. > >> b) We leave the current backing file untouched. > > Hm. That doesn't make sense for blockdev-add, so you could argue that > this behavior works as a default for reopen (because it cannot be > "confused" with the blockdev-add default). > >> c) We forbid it, and the user has to pass an explicit child, or NULL. > > That sounds good. > >> I chose (b) in this series. I suppose (c) could also be an option. But >> (a) doesn't looke like a good idea. > > I agree with the last sentiment, but I'd prefer making it an error > instead of choosing (b). Yes, you could argue that choosing (b) as a > default makes sense in a way, but in another, it just doesn't make > sense. (Because while (b) makes no sense for blockdev-add, (a) would > make sense for both blockdev-add and reopen. Sure, it's horrible to > support, but from a user's POV, it makes sense. So it's just > confusing not to make that the default for reopen as well). > > But the most important point is that it's trivial for the user to keep > the current backing file. They just need to give the current > backing's node-name.
Or NULL if there's no backing file, right? The problem I see with this is that it would make the options quite verbose. "backing" is an attribute of all BDSs, also protocol ones. I suppose we can make "backing" optional in those, or is there any case where it makes sense? Berto
