On Thu, Feb 02, 2017 at 02:56:51AM -0800, Christoph Hellwig wrote: > > I really wonder if this is the right approach. Most of the users of > > iov_iter_get_pages()/iov_iter_get_pages_alloc() look like they want > > something like > > iov_iter_for_each_page(iter, size, f, data) > > with int (*f)(struct page *page, size_t from, size_t size, void *data) > > passed as callback. Not everything fits that model, but there's a whole > > lot of things that do. > > I was planning to do that, mostly because of the iomap dio code that > would not only get a lot cleaner with this, but also support multi-page > bvecs that we hope to have in the block layer soon. The issue with it > is that we need to touch all the arch get_user_pages_fast > implementations, so it's going to be a relatively invasive change that I > didn't want to fix with just introducing the new direct I/O code. I'm not sure we need to touch any get_user_pages_fast() at all; let it fill a medium-sized array and use that as a buffer. In particular, I *really* don't like the idea of having the callbacks done in an inconsistent locking environment - sometimes under ->mmap_sem, sometimes not. I played with "let it fill bio_vec array", but it doesn't really fit the users; variant with callbacks is cleaner, IMO.
