[PATCH 1/4] fs: make do_loop_readv_writev() deal with ITER_UBUF

[Jens Axboe <axboe@kernel.dk>]

We caller this helper if we don't have a read_iter/write_iter available,
and it will go over the iov_iter manually copying data in/out as needed.
But it's currently assuming it's being passed an ITER_IOVEC. Enable
use of ITER_UBUF with this helper as well, in preparation for importing
single segment iovecs as ITER_UBUF.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/read_write.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 7a2ff6157eda..de9ce948d11a 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -748,10 +748,21 @@ static ssize_t do_loop_readv_writev(struct file *filp, struct iov_iter *iter,
 	if (flags & ~RWF_HIPRI)
 		return -EOPNOTSUPP;
 
+	if (WARN_ON_ONCE(iter->iter_type != ITER_IOVEC &&
+			 iter->iter_type != ITER_UBUF))
+		return -EINVAL;
+
 	while (iov_iter_count(iter)) {
-		struct iovec iovec = iov_iter_iovec(iter);
+		struct iovec iovec;
 		ssize_t nr;
 
+		if (iter_is_ubuf(iter)) {
+			iovec.iov_base = iter->ubuf + iter->iov_offset;
+			iovec.iov_len = iov_iter_count(iter);
+		} else {
+			iovec = iov_iter_iovec(iter);
+		}
+
 		if (type == READ) {
 			nr = filp->f_op->read(filp, iovec.iov_base,
 					      iovec.iov_len, ppos);
-- 
2.39.2