Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices

[Mike Snitzer <snitzer@redhat.com>]

On Mon, Jun 20 2016 at  6:22pm -0400,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Mon, Jun 20 2016 at  5:28pm -0400,
> Kani, Toshimitsu <toshi.kani@hpe.com> wrote:
> 
> > 
> > Hi Mike,
> > 
> > Can you fold the following patch to the dm-linear patch?
> > 
> > Thanks,
> > -Tsohi
> > 
> > ------
> > Subject: [PATCH] dm-linear: Fix partition handling for DAX
> > 
> > Partition handling was missing in linear_direct_access().
> > Call bdev_direct_access(), instead of directly calling
> > target direct_access function.
> > 
> > Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
> > ---
> >  drivers/md/dm-linear.c |   14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
> > index 325aa06..38323e4 100644
> > --- a/drivers/md/dm-linear.c
> > +++ b/drivers/md/dm-linear.c
> > @@ -148,10 +148,16 @@ static long linear_direct_access(struct dm_target *ti,
> > sector_t sector,
> >  {
> >  	struct linear_c *lc = ti->private;
> >  	struct block_device *bdev = lc->dev->bdev;
> > -	const struct block_device_operations *bd_ops = bdev->bd_disk->fops;
> > -
> > -	return bd_ops->direct_access(bdev, linear_map_sector(ti, sector),
> > -				     kaddr, pfn, size);
> > +	struct blk_dax_ctl dax = {
> > +		.sector = linear_map_sector(ti, sector),
> > +		.size = size,
> > +	};
> > +	long ret;
> > +
> > +	ret = bdev_direct_access(bdev, &dax);
> > +	*kaddr = dax.addr;
> > +	*pfn = dax.pfn;
> > +	return ret;
> >  }
> >  
> >  static struct target_type linear_target = {
> 
> Looks good, I folded it in and tested it to work.  Pushed to my 'wip'
> branch.
> 
> No longer seeing any corruption in my test that was using partitions to
> span pmem devices with a dm-linear device.
> 
> Jens, any chance you'd be open to picking up the first 2 patches in this
> series?  Or would you like to see them folded or something different?

I'm now wondering if we'd be better off setting a new QUEUE_FLAG_DAX
rather than establish GENHD_FL_DAX on the genhd?

It'd be quite a bit easier to allow upper layers (e.g. XFS and ext4) to
check for a queue flag.