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.
But if you still prefer to change it, I am open to make that change.
Thanks
Vivek
