io_uring/rsrc: separate kbuf offset adjustments

Kernel registered buffers are special because segments are not uniform
in size, and we have a bunch of optimisations based on that uniformity
for normal buffers. Handle kbuf separately, it'll be cleaner this way.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/4e9e5990b0ab5aee723c0be5cd9b5bcf810375f9.1744882081.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 4d62897d1c89e9ece881e77e30e946c388c60b93..fddde8ffe81e9873442754a7a9edf1e566dca0a5 100644 (file)
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1048,11 +1048,14 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
        if (!(imu->dir & (1 << ddir)))
                return -EFAULT;
 
-       /*
-        * Might not be a start of buffer, set size appropriately
-        * and advance us to the beginning.
-        */
        offset = buf_addr - imu->ubuf;
+
+       if (imu->is_kbuf) {
+               iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, offset + len);
+               iov_iter_advance(iter, offset);
+               return 0;
+       }
+
        iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, offset + len);
 
        /*
@@ -1072,17 +1075,9 @@ static int io_import_fixed(int ddir, struct iov_iter *iter,
         * be folio_size aligned.
         */
        bvec = imu->bvec;
-
-       /*
-        * Kernel buffer bvecs, on the other hand, don't necessarily
-        * have the size property of user registered ones, so we have
-        * 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);
        } else {
                unsigned long seg_skip;