FWIW, I'm not sure if skb_splice_bits() can't land us in trouble; fragments might come from compound pages and I'm not entirely convinced that we won't end up with coalesced fragments putting more than PAGE_SIZE into a single pipe_buffer. And that could badly confuse a bunch of code.
Can that legitimately happen? If so, we'll need to audit quite a few ->splice_write()-related codepaths; FUSE, in particular, is very likely to be unhappy with that kind of stuff, and it's not the only place where we might count upon never seeing e.g. longer than PAGE_SIZE chunks in bio_vec. It shouldn't be all that hard to fix, but if the whole thing is simply impossible, I would rather avoid that round of RTFS at the moment... Comments?
