[dm-devel] [PATCH 1/5] dax, pmem: Add a dax operation zero_page_range

[Vivek Goyal]

On Fri, Feb 07, 2020 at 08:57:39AM -0800, Dan Williams wrote:
> On Wed, Feb 5, 2020 at 11:41 PM Christoph Hellwig <hch at infradead.org> wrote:
> >
> > On Wed, Feb 05, 2020 at 04:40:44PM -0800, Dan Williams wrote:
> > > > I don't have any reason not to pass phys_addr_t. If that sounds better,
> > > > will make changes.
> > >
> > > The problem is device-mapper. That wants to use offset to route
> > > through the map to the leaf device. If it weren't for the firmware
> > > communication requirement you could do:
> > >
> > > dax_direct_access(...)
> > > generic_dax_zero_page_range(...)
> > >
> > > ...but as long as the firmware error clearing path is required I think
> > > we need to do pass the pgoff through the interface and do the pgoff to
> > > virt / phys translation inside the ops handler.
> >
> > Maybe phys_addr_t was the wrong type - but why do we split the offset
> > into the block device argument into a pgoff and offset into page instead
> > of a single 64-bit value?
> 
> Oh, got it yes, that looks odd for sub-page zeroing. Yes, let's just
> have one device relative byte-offset.

So what's the best type to represent this offset. "u64" or "phys_addr_t"
or "loff_t" or something else.  I like phys_addr_t followed by u64.

Vivek