Am 21.06.2016 um 13:01 hat Paolo Bonzini geschrieben: > On 21/06/2016 12:56, Kevin Wolf wrote: > > Am 21.06.2016 um 11:47 hat Paolo Bonzini geschrieben: > >> I still fail to understand what is the rationale for this change. The > >> API is weird; you read from a disk, not from an edge, and in fact the > >> first thing all the APIs do is dereference the BdrvChild... > >> > >> The assertions are nice, but I'm not sure it's a good idea to design a > >> whole API around them. > > > > Do you see a problem with such an API, though? If there is no reason not > > to have the advantages, as small as they may seem, why not take them? > > I don't see a reason not to take them; I don't see any red flags, but > there are some yellow flags (the kinda weird API) that I don't > understand and I hope you can explain. > > Thinking more about it, it's perfectly possible that this is just a > combination of block/io.c's growth by accretion and the well-known fact > "naming pseudo-OOP member functions in C sucks". > > In other words, if you sell me this as "let's add some member functions > to BdrvChild and use them", I can buy it. Perhaps the only thing to do > then is to rename functions and design a consistent naming.
Hm, I never thought about it this way, but I think it actually makes sense. As we want to represent a graph where both nodes and edges can have attributes and methods, OOP-wise both of them are objects, namely BDS and BdrvChild. So we have some BDS A that has a Child B, and Child B in turn has a BDS C. What we used to do is that A asks B for the node it points to (C), and then directly calls a method of C. After the conversion, A calls a method of B, which in turn forwards the request by calling a method of C, which is much more straightforward and ideally even allows the node that B points to to remain private (we're not quite there, though). Kevin