Hello, Kent. On Tue, Oct 02, 2012 at 08:00:20PM -0700, Kent Overstreet wrote: > > However, I don't think it's a good idea to try to implement something > > which is a neutral transport of opaque data between userland and lower > > layers. Things like that sound attractive with unlimited > > possibilities but reality seems to have the tendancy to make a big > > mess out of setups like that. > > I don't see how the "neutral transport of opaque data" itself is a bad > thing. We want something simple and sane to build actual interfaces on > top of - once we've got that, we can either build clean generic well > defined interfaces or we can make a mess like with ioctls :P > > It's like any other mechanism. There's good syscalls and bad syscalls... Depending on what a feature aims for, the design and implementation vary greatly. If you go for completely generic extensible stuff which can be used to warp space-time continuum, it's easy to end up with a monstrosity with generic and programmable parser, verifier, accessor and so on. > Say we implement an attr to control a block layer cache. That attr could > be parsed/validated in high level code (if there's any to do) - that I > don't object to. But the high level code isn't going to /know/ whether > there was any block cache in the stack that handled the attr. If the > attr is passed down to the block cache, that block cache can return that > it was handled. My point is that if it doesn't fit the generic abstract model as in fadvise(2), it probably isn't worth supporting in any generic manner. > > It's okay to allow some side channel thing for specific hacky uses but > > I really hope the general design were focused around properly > > abstracted attributes which can be understood and handled by the upper > > layer. > > Completely agreed. I want to leave that side channel open for > experimentation, and so we have a way of implementing one off hacky > stuff when we need to - but normal mainline stuff should be sane and > well designed. So, I think we can aim for something simple and modest (the only thing I can think of at the moment is task association) and provide simple framework which can be used for specific custom usages. Let's please not go overboard with generic parser / verifier which supports pointer indirection or whatnot. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
