linux-kernel - Re: [RFC V2 11/18] famfs_fuse: Basic famfs mount opts

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] [day] [month] [year] [list]

Message-ID: <20250712055405.GK2672029@frogsfrogsfrogs>
Date: Fri, 11 Jul 2025 22:54:05 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: John Groves <John@...ves.net>
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>,
	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>,
	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 11/18] famfs_fuse: Basic famfs mount opts

On Fri, Jul 11, 2025 at 10:28:20AM -0500, John Groves wrote:
> On 25/07/08 08:59PM, Darrick J. Wong wrote:
> > On Thu, Jul 03, 2025 at 01:50:25PM -0500, John Groves wrote:
> > > * -o shadow=<shadowpath>
> > 
> > What is a shadow?
> > 
> > > * -o daxdev=<daxdev>
> 
> Derp - OK, that's a stale commit message. Here is the one for the -next
> version of this patch:
> 
>     famfs_fuse: Basic famfs mount opt: -o shadow=<shadowpath>
> 
>     The shadow path is a (usually tmpfs) file system area used by the famfs 
>     user space to commuicate with the famfs fuse server. There is a minor 
>     dilemma that the user space tools must be able to resolve from a mount 
>     point path to a shadow path. The shadow path is exposed via /proc/mounts, 
>     but otherwise not used by the kernel. User space gets the shadow path 
>     from /proc/mounts...

Ah.  A service directory, of sorts.

> > And, uh, if there's a FUSE_GET_DAXDEV command, then what does this mount
> > option do?  Pre-populate the first element of that set?
> > 
> > --D
> > 
> 
> I took out -o daxdev, but had failed to update the commit msg.
> 
> The logic is this: The general model requires the FUSE_GET_DAXDEV message /
> response, so passing in the primary daxdev as a -o arg creates two ways to
> do the same thing.
> 
> The only initial heartburn about this was one could imagine a case where a
> mount happens, but no I/O happens for a while so the mount could "succeed",
> only to fail later if the primary daxdev could not be accessed.
> 
> But this can't happen with famfs, because the mount procedure includes 
> creating "meta files" - .meta/.superblock and .meta/.log and accessing them
> immediately. So it is guaranteed that FUSE_GET_DAXDEV will be sent right away,
> and if it fails, the mount will be unwound.

<nod> 

--D

> Thanks Darrick!
> John
> 
> <snip>
> 
>