linux-kernel - Re: [RFC V2 12/18] famfs_fuse: Plumb the GET

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <gwjcw52itbe4uyr2ttwvv2gjain7xyteicox5jhoqjkr23bhef@xfz6ikusckll>
Date: Fri, 4 Jul 2025 19:06:32 -0500
From: John Groves <John@...ves.net>
To: Amir Goldstein <amir73il@...il.com>
Cc: Dan Williams <dan.j.williams@...el.com>, 
	Miklos Szeredi <miklos@...redi.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, 
	Jonathan Cameron <Jonathan.Cameron@...wei.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 12/18] famfs_fuse: Plumb the GET_FMAP message/response

On 25/07/04 03:30PM, John Groves wrote:
> On 25/07/04 10:54AM, Amir Goldstein wrote:
> > On Thu, Jul 3, 2025 at 8:51 PM John Groves <John@...ves.net> wrote:
> > >
> > > Upon completion of an OPEN, if we're in famfs-mode we do a GET_FMAP to
> > > retrieve and cache up the file-to-dax map in the kernel. If this
> > > succeeds, read/write/mmap are resolved direct-to-dax with no upcalls.
> > >
> > > GET_FMAP has a variable-size response payload, and the allocated size
> > > is sent in the in_args[0].size field. If the fmap would overflow the
> > > message, the fuse server sends a reply of size 'sizeof(uint32_t)' which
> > > specifies the size of the fmap message. Then the kernel can realloc a
> > > large enough buffer and try again.
> > >
> > > Signed-off-by: John Groves <john@...ves.net>
> > > ---
> > >  fs/fuse/file.c            | 84 +++++++++++++++++++++++++++++++++++++++
> > >  fs/fuse/fuse_i.h          | 36 ++++++++++++++++-
> > >  fs/fuse/inode.c           | 19 +++++++--
> > >  fs/fuse/iomode.c          |  2 +-
> > >  include/uapi/linux/fuse.h | 18 +++++++++
> > >  5 files changed, 154 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> > > index 93b82660f0c8..8616fb0a6d61 100644
> > > --- a/fs/fuse/file.c
> > > +++ b/fs/fuse/file.c
> > > @@ -230,6 +230,77 @@ static void fuse_truncate_update_attr(struct inode *inode, struct file *file)
> > >         fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
> > >  }
> > >
> > > +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> > 
> > We generally try to avoid #ifdef blocks in c files
> > keep them mostly in h files and use in c files
> >    if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX))
> > 
> > also #if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> > it a bit strange for a bool Kconfig because it looks too
> > much like the c code, so I prefer
> > #ifdef CONFIG_FUSE_FAMFS_DAX
> > when you have to use it
> > 
> > If you need entire functions compiled out, why not put them in famfs.c?
> 
> Perhaps moving fuse_get_fmap() to famfs.c is the best approach. Will try that
> first.
> 
> Regarding '#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)', vs.
> '#ifdef CONFIG_FUSE_FAMFS_DAX' vs. '#if CONFIG_FUSE_FAMFS_DAX'...
> 
> I've learned to be cautious there because the latter two are undefined if
> CONFIG_FUSE_FAMFS_DAX=m. I've been burned by this.
> 
> My original thinking was that famfs made sense as a module, but I'm leaning
> the other way now - and in this series fs/fuse/Kconfig makes it a bool - 
> meaning all three macro tests will work because a bool can't be set to 'm'. 
> 
> So to the extent that I need conditional compilation macros I can switch
> to '#ifdef...'.

Doh. Spirit of full disclosure: this commit doesn't build if
CONFIG_FUSE_FAMFS_DAX is not set (!=y). So the conditionals are at
risk if getting worse, not better. Working on it...

<snip>

Thanks,
John