io_uring: do not always copy iovec in io_req_map_rw()

In io_read_prep() or io_write_prep(), io_req_map_rw() takes
struct io_async_rw's fast_iov as argument to call io_import_iovec(),
and if io_import_iovec() uses struct io_async_rw's fast_iov as
valid iovec array, later indeed io_req_map_rw() does not need
to do the memcpy operation, because they are same pointers.

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e71aa42e102ab546e64f58f39edbce17be1fa297..b06188a50af449e23902a8f90e4668bb8b7ae9ac 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2493,8 +2493,9 @@ static void io_req_map_rw(struct io_kiocb *req, ssize_t io_size,
        req->io->rw.iov = iovec;
        if (!req->io->rw.iov) {
                req->io->rw.iov = req->io->rw.fast_iov;
-               memcpy(req->io->rw.iov, fast_iov,
-                       sizeof(struct iovec) * iter->nr_segs);
+               if (req->io->rw.iov != fast_iov)
+                       memcpy(req->io->rw.iov, fast_iov,
+                              sizeof(struct iovec) * iter->nr_segs);
        } else {
                req->flags |= REQ_F_NEED_CLEANUP;
        }