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

[Karel Zak <kzak@redhat.com>]

On Tue, Nov 10, 2015 at 02:05:39PM +0800, Ming Lei wrote:
> On Mon, Nov 9, 2015 at 7:46 PM, Karel Zak <kzak@redhat.com> wrote:
> > 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;
> 
> I don't think this change is doable because lo_flags is always started
> as zero from loop_set_fd().

 Sorry, wrong function -- should be loop_set_status() where we can
 modify lo->lo_flags by info->lo_flags. It's already used for
 LO_FLAGS_AUTOCLEAR and LO_FLAGS_PARTSCAN.

    Karel

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