Pull io_uring iov_iter retry fixes from Jens Axboe:
 "This adds a helper to save/restore iov_iter state, and modifies
  io_uring to use it.

  After that is done, we can now kill the iter->truncated addition that
  we added for this release. The io_uring change is being overly
  cautious with the save/restore/advance, but better safe than sorry and
  we can always improve that and reduce the overhead if it proves to be
  of concern. The only case to be worried about in this regard is huge
  IO, where iteration can take a while to iterate segments.

  I spent some time writing test cases, and expanded the coverage quite
  a bit from the last posting of this. liburing carries this regression
  test case now:

      https://git.kernel.dk/cgit/liburing/tree/test/file-verify.c

  which exercises all of this. It now also supports provided buffers,
  and explicitly tests for end-of-file/device truncation as well.

  On top of that, Pavel s...