Re: [PATCH 0/2] losetup: support direct-IO to backing file

[Karel Zak <kzak@redhat.com>]

On Mon, Nov 09, 2015 at 07:29:21PM +0800, Ming Lei wrote:
> > It's fine to use --direct-io as toggle, but it would be nice to
> > support it also when initialize the device.
> 
> OK, looks a good idea, but we still need to support the standalone
> command for direct-io for the case of 'mount -o loop'.

Sure, I understand this use-case. I have talked bout loop_set_fd(),
maybe all we need is:


diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 423f4ca..22642a0 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -925,7 +925,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 
 	set_device_ro(bdev, (lo_flags & LO_FLAGS_READ_ONLY) != 0);
 
-	lo->use_dio = false;
+	lo->use_dio = (lo_flags & LO_FLAGS_DIRECT_IO);
 	lo->lo_blocksize = lo_blocksize;
 	lo->lo_device = bdev;
 	lo->lo_flags = lo_flags;


then we can a little bit modify your losetup.c patches and support
--direct-io also for A_CREATE.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com