linux-kernel - Re: [PATCH V3 15/21] famfs_fuse: Create files with famfs fmaps

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Message-ID: <smqodjljwvhnssmq4ho3hicnomzyrpsawy65ykxhigrjl7yawu@xwtbxjamivk7>
Date: Wed, 7 Jan 2026 15:30:46 -0600
From: John Groves <John@...ves.net>
To: Miklos Szeredi <miklos@...redi.hu>, 
	Dan Williams <dan.j.williams@...el.com>, Bernd Schubert <bschubert@....com>, 
	Alison Schofield <alison.schofield@...el.com>
Cc: 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>, Jonathan Cameron <Jonathan.Cameron@...wei.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 15/21] famfs_fuse: Create files with famfs fmaps

On 26/01/07 09:33AM, John Groves wrote:
> On completion of GET_FMAP message/response, setup the full famfs
> metadata such that it's possible to handle read/write/mmap directly to
> dax. Note that the devdax_iomap plumbing is not in yet...
> 
> * Add famfs_kfmap.h: in-memory structures for resolving famfs file maps
>   (fmaps) to dax.
> * famfs.c: allocate, initialize and free fmaps
> * inode.c: only allow famfs mode if the fuse server has CAP_SYS_RAWIO
> * Update MAINTAINERS for the new files.
> 
> Signed-off-by: John Groves <john@...ves.net>
> ---
>  MAINTAINERS               |   1 +
>  fs/fuse/famfs.c           | 355 +++++++++++++++++++++++++++++++++++++-
>  fs/fuse/famfs_kfmap.h     |  67 +++++++
>  fs/fuse/fuse_i.h          |  22 ++-
>  fs/fuse/inode.c           |  21 ++-
>  include/uapi/linux/fuse.h |  56 ++++++
>  6 files changed, 510 insertions(+), 12 deletions(-)
>  create mode 100644 fs/fuse/famfs_kfmap.h
> 

[ ... ]

> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 9e121a1d63b7..391ead26bfa2 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -121,7 +121,7 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
>  		fuse_inode_backing_set(fi, NULL);
>  
>  	if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX))
> -		famfs_meta_set(fi, NULL);
> +		famfs_meta_init(fi);
>  
>  	return &fi->inode;
>  
> @@ -1485,8 +1485,21 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
>  				timeout = arg->request_timeout;
>  
>  			if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX) &&
> -			    flags & FUSE_DAX_FMAP)
> -				fc->famfs_iomap = 1;
> +			    flags & FUSE_DAX_FMAP) {
> +				/* famfs_iomap is only allowed if the fuse
> +				 * server has CAP_SYS_RAWIO. This was checked
> +				 * in fuse_send_init, and FUSE_DAX_IOMAP was
> +				 * set in in_flags if so. Only allow enablement
> +				 * if we find it there. This function is
> +				 * normally not running in fuse server context,
> +				 * so we can do the capability check here...
                                         ^^^
Oops: this should be "can't" - we can't do the capability check here since we're not in
fuse server context. Will fix before merge...

[ ... ]

John