Revert "io_uring/rsrc: simplify the bvec iter count calculation"

This reverts commit 2a51c327d4a4a2eb62d67f4ea13a17efd0f25c5c.

The kernel registered bvecs do use the iov_iter_advance() API, so we
can't rely on this simplification anymore.

Fixes: 27cb27b6d5ea40 ("io_uring: add support for kernel registered bvecs")
Reported-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://lore.kernel.org/r/20250310184825.569371-1-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 5dd1e082755946f224b5f047b073f6ebb97771d5..5fff6ba2b7c05cb75d9099d4fae111200cd8ab1c 100644 (file)
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1024,7 +1024,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
         * and advance us to the beginning.
         */
        offset = buf_addr - imu->ubuf;
-       iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, len);
+       iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, offset + len);
 
        if (offset) {
                /*
@@ -1051,6 +1051,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
                 * to use the slow iter advance.
                 */
                if (offset < bvec->bv_len) {
+                       iter->count -= offset;
                        iter->iov_offset = offset;
                } else if (imu->is_kbuf) {
                        iov_iter_advance(iter, offset);
@@ -1063,6 +1064,7 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
 
                        iter->bvec += seg_skip;
                        iter->nr_segs -= seg_skip;
+                       iter->count -= bvec->bv_len + offset;
                        iter->iov_offset = offset & ((1UL << imu->folio_shift) - 1);
                }
        }