linux-kernel - Re: kdbus: add node and filesystem implementation

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Date:	Fri, 21 Nov 2014 08:35:11 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tom Gundersen <teg@...m.no>, Jiri Kosina <jkosina@...e.cz>,
	Linux API <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: Re: kdbus: add node and filesystem implementation

On Thu, Nov 20, 2014 at 9:02 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> From: Daniel Mack <daniel@...que.org>
>
> kdbusfs is a filesystem that will expose a fresh kdbus domain context
> each time it is mounted. Per mount point, there will be a 'control'
> node, which can be used to create buses. fs.c contains the
> implementation of that pseudo-fs. Exported inodes of 'file' type have
> their i_fop set to either kdbus_handle_control_ops or
> kdbus_handle_ep_ops, depending on their type. The actual dispatching
> of file operations is done from handle.c
>
> node.c is an implementation of a kdbus object that has an id and
> children, organized in an R/B tree. The tree is used by the filesystem
> code for lookup and iterator functions, and to deactivate children
> once the parent is deactivated. Every inode exported by kdbusfs is
> backed by a kdbus_node, hence it is embedded in struct kdbus_ep,
> struct kdbus_bus and struct kdbus_domain.
>
> Signed-off-by: Daniel Mack <daniel@...que.org>
> Signed-off-by: David Herrmann <dh.herrmann@...il.com>
> Signed-off-by: Djalal Harouni <tixxdz@...ndz.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---


> +
> +static struct file_system_type fs_type = {
> +       .name           = KBUILD_MODNAME "fs",
> +       .owner          = THIS_MODULE,
> +       .mount          = fs_super_mount,
> +       .kill_sb        = fs_super_kill,
> +};

Does this want something like:

.fs_flags = FS_USERNS_MOUNT

This design may have the annoying property that, if a namespace-based
sandbox wants to use kdbus itself, it will need to proxy anything from
the parent that it wants to use.

Is there a good reason why individual *busses* don't show up in the
filesystem?  If they did, maybe they could be bind-mounted or
otherwise arranged to cross namespace boundaries.

--Andy
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