Merge tag 'iov_iter.3-5.15-2021-09-17' of git://git.kernel.dk/linux-block

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 sanitized the IOPOLL retry path to follow the
  exact same pattern as normal IO"

* tag 'iov_iter.3-5.15-2021-09-17' of git://git.kernel.dk/linux-block:
  io_uring: move iopoll reissue into regular IO path
  Revert "iov_iter: track truncated size"
  io_uring: use iov_iter state save/restore helpers
  iov_iter: add helper to save iov_iter state

1 files changed, 16 insertions, 5 deletions

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 5265024e8b90..207101a9c5c3 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -27,6 +27,12 @@ enum iter_type {
 	ITER_DISCARD,
 };
 
+struct iov_iter_state {
+	size_t iov_offset;
+	size_t count;
+	unsigned long nr_segs;
+};
+
 struct iov_iter {
 	u8 iter_type;
 	bool data_source;
@@ -47,7 +53,6 @@ struct iov_iter {
 		};
 		loff_t xarray_start;
 	};
-	size_t truncated;
 };
 
 static inline enum iter_type iov_iter_type(const struct iov_iter *i)
@@ -55,6 +60,14 @@ static inline enum iter_type iov_iter_type(const struct iov_iter *i)
 	return i->iter_type;
 }
 
+static inline void iov_iter_save_state(struct iov_iter *iter,
+				       struct iov_iter_state *state)
+{
+	state->iov_offset = iter->iov_offset;
+	state->count = iter->count;
+	state->nr_segs = iter->nr_segs;
+}
+
 static inline bool iter_is_iovec(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_IOVEC;
@@ -233,6 +246,7 @@ ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages,
 ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, struct page ***pages,
 			size_t maxsize, size_t *start);
 int iov_iter_npages(const struct iov_iter *i, int maxpages);
+void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state);
 
 const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags);
 
@@ -255,10 +269,8 @@ static inline void iov_iter_truncate(struct iov_iter *i, u64 count)
 	 * conversion in assignement is by definition greater than all
 	 * values of size_t, including old i->count.
 	 */
-	if (i->count > count) {
-		i->truncated += i->count - count;
+	if (i->count > count)
 		i->count = count;
-	}
 }
 
 /*
@@ -267,7 +279,6 @@ static inline void iov_iter_truncate(struct iov_iter *i, u64 count)
  */
 static inline void iov_iter_reexpand(struct iov_iter *i, size_t count)
 {
-	i->truncated -= count - i->count;
 	i->count = count;
 }