direct-io: add flag to allow aio writes beyond i_size

Some filesystems can handle direct I/O writes beyond i_size safely,
so allow them to opt into receiving them.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 160a5489a939..a701752dd750 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1194,13 +1194,19 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
         }
 
         /*
-         * For file extending writes updating i_size before data
-         * writeouts complete can expose uninitialized blocks. So
-         * even for AIO, we need to wait for i/o to complete before
-         * returning in this case.
+         * For file extending writes updating i_size before data writeouts
+         * complete can expose uninitialized blocks in dumb filesystems.
+         * In that case we need to wait for I/O completion even if asked
+         * for an asynchronous write.
          */
-        dio->is_async = !is_sync_kiocb(iocb) && !((rw & WRITE) &&
-                (end > i_size_read(inode)));
+        if (is_sync_kiocb(iocb))
+                dio->is_async = false;
+        else if (!(dio->flags & DIO_ASYNC_EXTEND) &&
+            (rw & WRITE) && end > i_size_read(inode))
+                dio->is_async = false;
+        else
+                dio->is_async = true;
+
         dio->inode = inode;
         dio->rw = rw;