[PATCH] io_uring: do not always copy iovec in io_req_map_rw()

[PATCH] io_uring: do not always copy iovec in io_req_map_rw()

[Xiaoguang Wang]

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>
---
 fs/io_uring.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6ac830b2b4fb..5eeac5b8ccc6 100644
--- 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;
 	}
-- 
2.17.2

Re: [PATCH] io_uring: do not always copy iovec in io_req_map_rw()

[Jens Axboe]

On 4/8/20 7:29 AM, Xiaoguang Wang wrote:
> 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.

Applied, thanks.

-- 
Jens Axboe