Hi, ather than repeat the same blurb again, see the v2 posting here: https://lore.kernel.org/linux-fsdevel/20230327180449.87382-1-axboe@xxxxxxxxx/ tldr - turn single segment iovecs into ITER_UBUF rather than ITER_IOVEC, because they are more efficient. The main change since v4 is doing the overlay trick in the iov_iter, so that the first segment of the iovec overlaps nicely with the ubuf address and length. With that, we can drop any functional driver change, as the normal iteration should just work out with ubuf having the single segment. Replace he iter_is_iovec() check with a basic iter->user_backed instead. Unfortunately we can't make iov_iter_iovec() much prettier, as we have to return a copy of the current iovec as the offset has to be added... Include a block fix for a shoddy copy of an iterator, as that'll otherwise cause issues. Ran the liburing test cases and the previously indicated ltp cases that barfed, and everything looks rosy. Comments welcome - with the above approach, we don't ever return iter->__ubuf_iovec, it's really just there as an overlay filler. Maybe we can make that a bit more apparent. -- Jens Axboe
