On Tue, 11 Feb 2020 10:11:14 -0500
Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> On Mon, Feb 10, 2020 at 09:53:15PM +0100, Gerald Schaefer wrote:
> > On Fri, 7 Feb 2020 15:26:49 -0500
> > Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> >
> > > Add dax operation zero_page_range for dcssblk driver.
> > >
> > > CC: linux-s390@xxxxxxxxxxxxxxx
> > > Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> > > Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> > > ---
> > > drivers/s390/block/dcssblk.c | 17 +++++++++++++++++
> > > 1 file changed, 17 insertions(+)
> > >
> > > diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> > > index 63502ca537eb..331abab5d066 100644
> > > --- a/drivers/s390/block/dcssblk.c
> > > +++ b/drivers/s390/block/dcssblk.c
> > > @@ -57,11 +57,28 @@ static size_t dcssblk_dax_copy_to_iter(struct dax_device *dax_dev,
> > > return copy_to_iter(addr, bytes, i);
> > > }
> > >
> > > +static int dcssblk_dax_zero_page_range(struct dax_device *dax_dev, u64 offset,
> > > + size_t len)
> > > +{
> > > + long rc;
> > > + void *kaddr;
> > > + pgoff_t pgoff = offset >> PAGE_SHIFT;
> > > + unsigned page_offset = offset_in_page(offset);
> > > +
> > > + rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
> >
> > Why do you pass only 1 page as nr_pages argument for dax_direct_access()?
> > In some other patch in this series there is a comment that this will
> > currently only be used for one page, but support for more pages might be
> > added later. Wouldn't it make sense to rather use something like
> > PAGE_ALIGN(page_offset + len) >> PAGE_SHIFT instead of 1 here, so that
> > this won't have to be changed when callers will be ready to use it
> > with more than one page?
> >
> > Of course, I guess then we'd also need some check on the return value
> > from dax_direct_access(), i.e. if the returned available range is
> > large enough for the requested range.
>
> I left it at 1 page because that's the current limitation of this
> interface and there are no callers which are zeroing across page
> boundaries.
>
> I prefer to keep it this way and modify it when we are extending this
> interface to allow zeroing across page boundaries. Because even if I add
> that logic, I can't test it.
OK, fine with me.
Reviewed-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
