give ->direct_IO() a copy of iov_iter

the thing is, we want to advance what's given to ->direct_IO() as we
are forming the request; however, the callers care about the amount
of data actually transferred, not the amount we tried to transfer.
It's more convenient to allow ->direct_IO() instances do use
iov_iter_advance() on the copy of iov_iter, leaving the actual
advancing of the original to caller.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 7 insertions, 3 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 70c048ea36e0..866f4ae8223b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1699,8 +1699,10 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
                 size = i_size_read(inode);
                 retval = filemap_write_and_wait_range(mapping, pos,
                                         pos + count - 1);
-                if (!retval)
-                        retval = mapping->a_ops->direct_IO(READ, iocb, &i, pos);
+                if (!retval) {
+                        struct iov_iter data = i;
+                        retval = mapping->a_ops->direct_IO(READ, iocb, &data, pos);
+                }
 
                 if (retval > 0) {
                         *ppos = pos + retval;
@@ -2351,6 +2353,7 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from,
         ssize_t         written;
         size_t          write_len;
         pgoff_t         end;
+        struct iov_iter data;
 
         if (count != ocount)
                 from->nr_segs = iov_shorten((struct iovec *)from->iov, from->nr_segs, count);
@@ -2382,7 +2385,8 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from,
                 }
         }
 
-        written = mapping->a_ops->direct_IO(WRITE, iocb, from, pos);
+        data = *from;
+        written = mapping->a_ops->direct_IO(WRITE, iocb, &data, pos);
 
         /*
          * Finally, try again to invalidate clean pages which might have been