Re: qemu-emulated nfit devices disappeared

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

On Thu, Nov 4, 2021 at 10:20 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Thu, Nov 04, 2021 at 10:17:31AM -0700, Christoph Hellwig wrote:
> > On Thu, Nov 04, 2021 at 10:09:37AM -0700, Dan Williams wrote:
> > > Hmm, so the driver has 2 modes "labeled" and "label-less", in the
> > > labeled mode it waits for an explicit:
> > >
> > >     ndctl create-namespace
> > >
> > > ...to provision region capacity into a namespace. In label-less mode
> > > it just assumes that the boundaries of the region are the boundaries
> > > of the namespace. In this case it looks like the driver found a label
> > > index block with no namespaces defined so it's waiting for one to be
> > > created. Are you saying that the only thing you changed from a working
> > > config with defined namespace to this one was a kernel change? I.e.
> > > the content of those memory-backend files has not changed?
> >
> > Well, the config change is the only thing I though of as relevant.
> > The content of those files actually changes all the time, as I also
> > use them as the backing store for my qemu configs that use block
> > devices.  E.g. the previous run they did show up as NVMe devices.
>
> Ok, blowing the files away and recreating them makes the pmem
> devices show up again.
>

Cool, yeah, I was going to guess the label area might have been
clobbered, but there was just enough left to force the driver into
labeled mode. You can verify with something like:

ndctl read-labels -I -j all

...to see if nvdimms have label index blocks.