Re: [PATCH V7 05/19] dax: Add dax_operations for use by fs-dax on fsdev dax

John Groves
2026-02-18T00:39:20Z

On 26/02/13 03:23PM, Ira Weiny wrote:
> John Groves wrote:
> > From: John Groves <John@Groves.net>
> >
> > fsdev: Add dax_operations for use by famfs
> >
> > - These methods are based on pmem_dax_ops from drivers/nvdimm/pmem.c
> > - fsdev_dax_direct_access() returns the hpa, pfn and kva. The kva was
> > newly stored as dev_dax->virt_addr by dev_dax_probe().
> > - The hpa/pfn are used for mmap (dax_iomap_fault()), and the kva is used
> > for read/write (dax_iomap_rw())
> > - fsdev_dax_recovery_write() and dev_dax_zero_page_range() have not been
> > tested yet. I'm looking for suggestions as to how to test those.
> > - dax-private.h: add dev_dax->cached_size, which fsdev needs to
> > remember. The dev_dax size cannot change while a driver is bound
> > (dev_dax_resize returns -EBUSY if dev->driver is set). Caching the size
> > at probe time allows fsdev's direct_access path can use it without
> > acquiring dax_dev_rwsem (which isn't exported anyway).
> >
> > Signed-off-by: John Groves <john@groves.net>
>
> [snip]
>
> > +
> > +static long __fsdev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
> > + long nr_pages, enum dax_access_mode mode, void **kaddr,
> > + unsigned long *pfn)
> > +{
> > + struct dev_dax *dev_dax = dax_get_private(dax_dev);
> > + size_t size = nr_pages << PAGE_SHIFT;
> > + size_t offset = pgoff << PAGE_SHIFT;
> > + void *virt_addr = dev_dax->virt_addr + offset;
> > + phys_addr_t phys;
> > + unsigned long local_pfn;
> > +
> > + WARN_ON(!dev_dax->virt_addr);
>
> WARN_ON_ONCE. But frankly I'm pretty sure this is impossible to hit given
> the probe call, so best remove it. Also yall already used dev_dax->virt_addr
> above. And will hand back a bad address to the caller. So...

Good point - dropped it.

>
> > +
> > + phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT);
> > + if (phys == -1) {
> > + dev_dbg(&dev_dax->dev,
> > + "pgoff (%#lx) out of range\n", pgoff);
> > + return -ERANGE;
>
> EFAULT?

This feels like a judgment call, but I'm fine with it.
Changed to -EFAULT

>
> Ira
>
> [snip]

Thanks Ira!
John