iov_iter: convert import_single_range() to ITER_UBUF

JIRA: https://issues.redhat.com/browse/RHEL-87739

commit e03ad4e
Author: Jens Axboe <axboe@kernel.dk>
Date:   Fri Mar 24 14:35:49 2023 -0600

    iov_iter: convert import_single_range() to ITER_UBUF

    Since we're just importing a single vector, we don't have to turn it
    into an ITER_IOVEC. Instead turn it into an ITER_UBUF, which is cheaper
    to iterate.

    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

lib/iov_iter.c

@@ -1915,9 +1915,7 @@ int import_single_range(int rw, void __user *buf, size_t len,
 	if (unlikely(!access_ok(buf, len)))
 		return -EFAULT;
 
-	iov->iov_base = buf;
-	iov->iov_len = len;
-	iov_iter_init(i, rw, iov, 1, len);
+	iov_iter_ubuf(i, rw, buf, len);
 	return 0;
 }
 EXPORT_SYMBOL(import_single_range);