linux-kernel - Re: [PATCH v4 05/28] dax: Document dax dev range tuple

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Message-ID: <20241016164826.000068e9@Huawei.com>
Date: Wed, 16 Oct 2024 16:48:26 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Ira Weiny <ira.weiny@...el.com>
CC: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>, "Navneet
 Singh" <navneet.singh@...el.com>, Jonathan Corbet <corbet@....net>, "Andrew
 Morton" <akpm@...ux-foundation.org>, Dan Williams <dan.j.williams@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, "Alison Schofield"
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>,
	<linux-btrfs@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <nvdimm@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 05/28] dax: Document dax dev range tuple

On Fri, 11 Oct 2024 15:40:58 -0500
Ira Weiny <ira.weiny@...el.com> wrote:

> Jonathan Cameron wrote:
> > On Mon, 07 Oct 2024 18:16:11 -0500
> > Ira Weiny <ira.weiny@...el.com> wrote:
> >   
> > > The device DAX structure is being enhanced to track additional DCD
> > > information.
> > > 
> > > The current range tuple was not fully documented.  Document it prior to
> > > adding information for DC.
> > > 
> > > Suggested-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> > > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> > >   
> > Isn't this a nested struct?
> > https://docs.kernel.org/doc-guide/kernel-doc.html#nested-structs-unions
> > 
> > I'm not quite sure how we document when it's a nested pointer to a
> > a structure.  Is it the same as for a 'normal' nested struct?  
> 
> In this case I think it best to document the struct and just document the
> reference.  See below.
> 
> >     
> > > ---
> > > Changes:
> > > [iweiny: move to start of series]
> > > ---
> > >  drivers/dax/dax-private.h | 5 ++++-
> > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
> > > index 446617b73aea..ccde98c3d4e2 100644
> > > --- a/drivers/dax/dax-private.h
> > > +++ b/drivers/dax/dax-private.h
> > > @@ -58,7 +58,10 @@ struct dax_mapping {
> > >   * @dev - device core
> > >   * @pgmap - pgmap for memmap setup / lifetime (driver owned)
> > >   * @nr_range: size of @ranges
> > > - * @ranges: resource-span + pgoff tuples for the instance
> > > + * @ranges: range tuples of memory used
> > > + * @pgoff: page offset  
> >       @ranges.pgoff?
> > etc  
> 
> Ok yea.
> 
> As for the pointer to a structure.  I think the best thing to do is simply
> document that structure.
> 
> Something like this building on this patch:
> 
> 
> diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
> index ccde98c3d4e2..b9816c933575 100644
> --- a/drivers/dax/dax-private.h
> +++ b/drivers/dax/dax-private.h
> @@ -40,6 +40,12 @@ struct dax_region {
>         struct device *youngest;
>  };
>  
> +/**
> + * struct dax_mapping - device to display mapping range attributes
> + * @dev: device representing this range
> + * @range_id: index within dev_dax ranges array
> + * @id: ida of this mapping
> + */
>  struct dax_mapping {
>         struct device dev;
>         int range_id;
> @@ -59,9 +65,9 @@ struct dax_mapping {
>   * @pgmap - pgmap for memmap setup / lifetime (driver owned)
>   * @nr_range: size of @ranges
>   * @ranges: range tuples of memory used
> - * @pgoff: page offset
> - * @range: resource-span
> - * @mapping: device to assist in interrogating the range layout
> + * @ranges.pgoff: page offset
> + * @ranges.range: resource-span
> + * @ranges.mapping: reference to the dax_mapping for this range

Maybe just pull out definition of struct dev_dax_range?
Avoids this confusion and no particularly obvious reason why it
is embedded in the definition of dev_dax.

>   */
>  struct dev_dax {
>         struct dax_region *region;
>