linux-kernel - Re: [PATCH V3 4/4] fuse: add famfs DAX fmap support

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Message-ID: <2mr7vou7zeauqypqq3xay6wdmc6g2havk2e33cfphwylu7dnit@qk32hbe7zgy3>
Date: Sun, 11 Jan 2026 12:24:29 -0600
From: John Groves <John@...ves.net>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: Miklos Szeredi <miklos@...redi.hu>, 
	Dan Williams <dan.j.williams@...el.com>, Bernd Schubert <bschubert@....com>, 
	Alison Schofield <alison.schofield@...el.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>, David Hildenbrand <david@...nel.org>, 
	Christian Brauner <brauner@...nel.org>, "Darrick J . Wong" <djwong@...nel.org>, 
	Randy Dunlap <rdunlap@...radead.org>, Jeff Layton <jlayton@...nel.org>, 
	Amir Goldstein <amir73il@...il.com>, Stefan Hajnoczi <shajnocz@...hat.com>, 
	Joanne Koong <joannelkoong@...il.com>, Josef Bacik <josef@...icpanda.com>, 
	Bagas Sanjaya <bagasdotme@...il.com>, Chen Linxuan <chenlinxuan@...ontech.com>, 
	James Morse <james.morse@....com>, Fuad Tabba <tabba@...gle.com>, 
	Sean Christopherson <seanjc@...gle.com>, Shivank Garg <shivankg@....com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Gregory Price <gourry@...rry.net>, 
	Aravind Ramesh <arramesh@...ron.com>, Ajay Joshi <ajayjoshi@...ron.com>, venkataravis@...ron.com, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev, 
	linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V3 4/4] fuse: add famfs DAX fmap support

On 26/01/08 03:31PM, Jonathan Cameron wrote:
> On Wed,  7 Jan 2026 09:34:43 -0600
> John Groves <John@...ves.net> wrote:
> 
> > Add new FUSE operations and capability for famfs DAX file mapping:
> > 
> > - FUSE_CAP_DAX_FMAP: New capability flag at bit 32 (using want_ext/capable_ext
> >   fields) to indicate kernel and userspace support for DAX fmaps
> > 
> > - GET_FMAP: New operation to retrieve a file map for DAX-mapped files.
> >   Returns a fuse_famfs_fmap_header followed by simple or interleaved
> >   extent descriptors. The kernel passes the file size as an argument.
> > 
> > - GET_DAXDEV: New operation to retrieve DAX device info by index.
> >   Called when GET_FMAP returns an fmap referencing a previously
> >   unknown DAX device.
> > 
> > These operations enable FUSE filesystems to provide direct access
> > mappings to persistent memory, allowing the kernel to map files
> > directly to DAX devices without page cache intermediation.
> > 
> > Signed-off-by: John Groves <john@...ves.net>
> 
> 
> > ---
> >  include/fuse_common.h   |  5 +++++
> >  include/fuse_lowlevel.h | 37 +++++++++++++++++++++++++++++++++++++
> >  lib/fuse_lowlevel.c     | 31 ++++++++++++++++++++++++++++++-
> >  3 files changed, 72 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/fuse_common.h b/include/fuse_common.h
> > index 041188e..e428ddb 100644
> > --- a/include/fuse_common.h
> > +++ b/include/fuse_common.h
> > @@ -512,6 +512,11 @@ struct fuse_loop_config_v1 {
> >   */
> >  #define FUSE_CAP_OVER_IO_URING (1UL << 31)
> >  
> > +/**
> > + * handle files that use famfs dax fmaps
> > + */
> > +#define FUSE_CAP_DAX_FMAP (1UL<<32)
> 
> From the context above, looks like local style is spaces around <<

Fixed, thanks!

[ ... ]

John