linux-kernel - Re: [RFC PATCH 12/19] famfs_fuse: Plumb the GET

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Message-ID: <CAOQ4uxj73Z8Hee1U7LxABYKoHbowA4ARBFDv434yDq+qn5iMZw@mail.gmail.com>
Date: Thu, 22 May 2025 17:45:54 +0200
From: Amir Goldstein <amir73il@...il.com>
To: John Groves <John@...ves.net>
Cc: Joanne Koong <joannelkoong@...il.com>, 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>, Luis Henriques <luis@...lia.com>, 
	Randy Dunlap <rdunlap@...radead.org>, Jeff Layton <jlayton@...nel.org>, 
	Kent Overstreet <kent.overstreet@...ux.dev>, Petr Vorel <pvorel@...e.cz>, 
	Brian Foster <bfoster@...hat.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, 
	Jonathan Cameron <Jonathan.Cameron@...wei.com>, Stefan Hajnoczi <shajnocz@...hat.com>, 
	Josef Bacik <josef@...icpanda.com>, Aravind Ramesh <arramesh@...ron.com>, 
	Ajay Joshi <ajayjoshi@...ron.com>
Subject: Re: [RFC PATCH 12/19] famfs_fuse: Plumb the GET_FMAP message/response

On Mon, May 12, 2025 at 6:28 PM John Groves <John@...ves.net> wrote:
>
> On 25/05/01 10:48PM, Joanne Koong wrote:
> > On Sun, Apr 20, 2025 at 6:34 PM John Groves <John@...ves.net> wrote:
> > >
> > > Upon completion of a LOOKUP, 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.
> > >
> > > Signed-off-by: John Groves <john@...ves.net>
> > > ---
...
> > > diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> > > index 7f4b73e739cb..848c8818e6f7 100644
> > > --- a/fs/fuse/inode.c
> > > +++ b/fs/fuse/inode.c
> > > @@ -117,6 +117,9 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
> > >         if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
> > >                 fuse_inode_backing_set(fi, NULL);
> > >
> > > +       if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX))
> > > +               famfs_meta_set(fi, NULL);
> >
> > "fi->famfs_meta = NULL;" looks simpler here
>
> I toootally agree here, but I was following the passthrough pattern
> just above.  @miklos or @Amir, got a preference here?
>

It's not about preference, this fails build.
Even though compiler (or pre-processor whatever) should be able to skip
"fi->famfs_meta = NULL;" if CONFIG_FUSE_FAMFS_DAX is not defined
IIRC it does not. Feel free to try. Maybe I do not remember correctly.

Thanks,
Amir.