linux-kernel - Re: [RFC V2 02/18] dev_dax_iomap: Add fs_dax_get() func to prepare dax for fs-dax usage

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Message-ID: <or7rm2n4syer4uxaubtotarjtmmilhedih4odgiwvqb4cfkvsl@5w66of2xms5l>
Date: Fri, 4 Jul 2025 07:54:38 -0500
From: John Groves <John@...ves.net>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: Dan Williams <dan.j.williams@...el.com>, 
	Miklos Szeredi <miklos@...redb.hu>, Bernd Schubert <bschubert@....com>, 
	John Groves <jgroves@...ron.com>, Jonathan Corbet <corbet@....net>, 
	Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, 
	Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, 
	"Darrick J . Wong" <djwong@...nel.org>, Randy Dunlap <rdunlap@...radead.org>, 
	Jeff Layton <jlayton@...nel.org>, Kent Overstreet <kent.overstreet@...ux.dev>, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev, 
	linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	Amir Goldstein <amir73il@...il.com>, Stefan Hajnoczi <shajnocz@...hat.com>, 
	Joanne Koong <joannelkoong@...il.com>, Josef Bacik <josef@...icpanda.com>, 
	Aravind Ramesh <arramesh@...ron.com>, Ajay Joshi <ajayjoshi@...ron.com>
Subject: Re: [RFC V2 02/18] dev_dax_iomap: Add fs_dax_get() func to prepare
 dax for fs-dax usage

On 25/07/04 11:39AM, Jonathan Cameron wrote:
> On Thu,  3 Jul 2025 13:50:16 -0500
> John Groves <John@...ves.net> wrote:
> 
> > This function should be called by fs-dax file systems after opening the
> > devdax device. This adds holder_operations, which effects exclusivity
> > between callers of fs_dax_get().
> > 
> > This function serves the same role as fs_dax_get_by_bdev(), which dax
> > file systems call after opening the pmem block device.
> > 
> > This also adds the CONFIG_DEV_DAX_IOMAP Kconfig parameter
> > 
> > Signed-off-by: John Groves <john@...ves.net>
> Trivial stuff inline.
> 
> 
> > ---
> >  drivers/dax/Kconfig |  6 ++++++
> >  drivers/dax/super.c | 30 ++++++++++++++++++++++++++++++
> >  include/linux/dax.h |  5 +++++
> >  3 files changed, 41 insertions(+)
> > 
> > diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
> > index d656e4c0eb84..ad19fa966b8b 100644
> > --- a/drivers/dax/Kconfig
> > +++ b/drivers/dax/Kconfig
> > @@ -78,4 +78,10 @@ config DEV_DAX_KMEM
> >  
> >  	  Say N if unsure.
> >  
> > +config DEV_DAX_IOMAP
> > +       depends on DEV_DAX && DAX
> > +       def_bool y
> > +       help
> > +         Support iomap mapping of devdax devices (for FS-DAX file
> > +         systems that reside on character /dev/dax devices)
> >  endif
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index e16d1d40d773..48bab9b5f341 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -122,6 +122,36 @@ void fs_put_dax(struct dax_device *dax_dev, void *holder)
> >  EXPORT_SYMBOL_GPL(fs_put_dax);
> >  #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
> >  
> > +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
> > +/**
> > + * fs_dax_get()
> 
> Trivial but from what I recall kernel-doc isn't going to like this.
> Needs a short description.

Right you are. I thought I'd checked all those, but missed this one.
Queued to -next.

> 
> > + *
> > + * fs-dax file systems call this function to prepare to use a devdax device for
> > + * fsdax. This is like fs_dax_get_by_bdev(), but the caller already has struct
> > + * dev_dax (and there  * is no bdev). The holder makes this exclusive.
> 
> there is no *bdev?  So * in wrong place.

I think that's a line-break-refactor malfunction on my part. Aueued to -next.

Thanks,
John