Re: [PATCH v5 1/4] nvdimm: Consider probe return -EOPNOTSUPP as success

[Dan Williams <dan.j.williams@intel.com>]

On Mon, Aug 19, 2019 at 12:07 AM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> Dan Williams <dan.j.williams@intel.com> writes:
>
> > On Tue, Aug 13, 2019 at 9:22 PM Dan Williams <dan.j.williams@intel.com> wrote:
> >>
> >> Hi Aneesh, logic looks correct but there are some cleanups I'd like to
> >> see and a lead-in patch that I attached.
> >>
> >> I've started prefixing nvdimm patches with:
> >>
> >>     libnvdimm/$component:
> >>
> >> ...since this patch mostly impacts the pmem driver lets prefix it
> >> "libnvdimm/pmem: "
> >>
> >> On Fri, Aug 9, 2019 at 12:45 AM Aneesh Kumar K.V
> >> <aneesh.kumar@linux.ibm.com> wrote:
> >> >
> >> > This patch add -EOPNOTSUPP as return from probe callback to
> >>
> >> s/This patch add/Add/
> >>
> >> No need to say "this patch" it's obviously a patch.
> >>
> >> > indicate we were not able to initialize a namespace due to pfn superblock
> >> > feature/version mismatch. We want to consider this a probe success so that
> >> > we can create new namesapce seed and there by avoid marking the failed
> >> > namespace as the seed namespace.
> >>
> >> Please replace usage of "we" with the exact agent involved as which
> >> "we" is being referred to gets confusing for the reader.
> >>
> >> i.e. "indicate that the pmem driver was not..." "The nvdimm core wants
> >> to consider this...".
> >>
> >> >
> >> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> >> > ---
> >> >  drivers/nvdimm/bus.c  |  2 +-
> >> >  drivers/nvdimm/pmem.c | 26 ++++++++++++++++++++++----
> >> >  2 files changed, 23 insertions(+), 5 deletions(-)
> >> >
> >> > diff --git a/drivers/nvdimm/bus.c b/drivers/nvdimm/bus.c
> >> > index 798c5c4aea9c..16c35e6446a7 100644
> >> > --- a/drivers/nvdimm/bus.c
> >> > +++ b/drivers/nvdimm/bus.c
> >> > @@ -95,7 +95,7 @@ static int nvdimm_bus_probe(struct device *dev)
> >> >         rc = nd_drv->probe(dev);
> >> >         debug_nvdimm_unlock(dev);
> >> >
> >> > -       if (rc == 0)
> >> > +       if (rc == 0 || rc == -EOPNOTSUPP)
> >> >                 nd_region_probe_success(nvdimm_bus, dev);
> >>
> >> This now makes the nd_region_probe_success() helper obviously misnamed
> >> since it now wants to take actions on non-probe success. I attached a
> >> lead-in cleanup that you can pull into your series that renames that
> >> routine to nd_region_advance_seeds().
> >>
> >> When you rebase this needs a comment about why EOPNOTSUPP has special handling.
> >>
> >> >         else
> >> >                 nd_region_disable(nvdimm_bus, dev);
> >> > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> >> > index 4c121dd03dd9..3f498881dd28 100644
> >> > --- a/drivers/nvdimm/pmem.c
> >> > +++ b/drivers/nvdimm/pmem.c
> >> > @@ -490,6 +490,7 @@ static int pmem_attach_disk(struct device *dev,
> >> >
> >> >  static int nd_pmem_probe(struct device *dev)
> >> >  {
> >> > +       int ret;
> >> >         struct nd_namespace_common *ndns;
> >> >
> >> >         ndns = nvdimm_namespace_common_probe(dev);
> >> > @@ -505,12 +506,29 @@ static int nd_pmem_probe(struct device *dev)
> >> >         if (is_nd_pfn(dev))
> >> >                 return pmem_attach_disk(dev, ndns);
> >> >
> >> > -       /* if we find a valid info-block we'll come back as that personality */
> >> > -       if (nd_btt_probe(dev, ndns) == 0 || nd_pfn_probe(dev, ndns) == 0
> >> > -                       || nd_dax_probe(dev, ndns) == 0)
> >>
> >> Similar need for an updated comment here to explain the special
> >> translation of error codes.
> >>
> >> > +       ret = nd_btt_probe(dev, ndns);
> >> > +       if (ret == 0)
> >> >                 return -ENXIO;
> >> > +       else if (ret == -EOPNOTSUPP)
> >>
> >> Are there cases where the btt driver needs to return EOPNOTSUPP? I'd
> >> otherwise like to keep this special casing constrained to the pfn /
> >> dax info block cases.
> >
> > In fact I think EOPNOTSUPP is only something that the device-dax case
> > would be concerned with because that's the only interface that
> > attempts to guarantee a given mapping granularity.
>
> We need to do similar error handling w.r.t fsdax when the pfn superblock
> indicates different PAGE_SIZE and struct page size?

Only in the case where PAGE_SIZE is less than the pfn superblock page
size, the memmap is stored on pmem, and the reservation is too small.
Otherwise the PAGE_SIZE difference does not matter in practice for the
fsdax case... unless I'm overlooking another failure case?

> I don't think btt
> needs to support EOPNOTSUPP. But we can keep it for consistency?

That's not a sufficient argument in my mind. The comment about why
EOPNOTSUPP is treated specially should have a note about the known
usages, and since there is no BTT case for it lets leave it out.