linux-kernel - Re: [PATCH] libnvdimm: Clarify nd_pfn

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Message-ID: <CAPcyv4jXS-doCdyTrcV3DL63N-q4m1H2=Msgm1z88HnF8bcEig@mail.gmail.com>
Date:   Mon, 21 Jan 2019 16:29:08 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Wei Yang <richardw.yang@...ux.intel.com>
Cc:     linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libnvdimm: Clarify nd_pfn_init() flow

On Mon, Jan 21, 2019 at 4:26 PM Wei Yang <richardw.yang@...ux.intel.com> wrote:
[..]
> >@@ -706,6 +711,22 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
> >               sig = DAX_SIG;
> >       else
> >               sig = PFN_SIG;
> >+
> >+      /*
> >+       * Check for an existing 'pfn' superblock before writing a new
> >+       * one. The intended flow is that on the first probe of an
> >+       * nd_{pfn,dax} device the superblock is calculated and written
> >+       * to the namespace. In this case nd_pfn_validate() returns
> >+       * -ENODEV because no valid superblock exists currently.
>
> As you replied in following mail:
>
> 3/ If present, nd_pfn_validate() returns 0 and nd_dax_probe()
> registers the dax0.1 device (this is a libnvdimm 'personality device).
>
> So at this point, nd_pfn_validate() return 0 or -ENODEV?

In this case 0, because the configuration was successfully validated.

-ENODEV, is only returned for the initial case where we want the
kernel to write the configuration.

All other error codes are an actual failure and the probe procedure stops.