On Fri, Jul 01, 2022 at 08:08:37PM +0100, Al Viro wrote: > On Fri, Jul 01, 2022 at 12:38:36PM -0600, Keith Busch wrote: > > > size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset); > > > - if (size > 0) > > > - size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev)); > > > if (unlikely(size <= 0)) > > > return size ? size : -EFAULT; > > > + nr_pages = DIV_ROUND_UP(offset + size, PAGE_SIZE); > > > > > > + size = ALIGN_DOWN(size, bdev_logical_block_size(bio->bi_bdev)); > > > > We still need to return EFAULT if size becomes 0 because that's the only way > > bio_iov_iter_get_pages()'s loop will break out in this condition. > > I really don't like these calling conventions ;-/ No argument here; I'm just working in the space as I found it. :) > What do you want to happen if we have that align-down to reduce size? > IOW, what should be the state after that loop in the caller? We fill up the bio to bi_max_vecs. If there are more pages than vectors, then the bio is submitted as-is with the partially drained iov_iter. The remainder of the iov is left for a subsequent bio to deal with. The ALIGN_DOWN is required because I've replaced the artificial kernel aligment with the underlying hardware's alignment. The hardware's alignment is usually smaller than a block size. If the last bvec has a non-block aligned offset, then it has to be truncated down, which could result in a 0 size when bi_vcnt is already non-zero. If that happens, we just submit the bio as-is, and allocate a new one to deal with the rest of the iov.
