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

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Message-ID: <CANq1E4T9nJSAC2VprUXpCdCFPE+mzNSEzi+z78HdYU_OiYC=wA@mail.gmail.com>
Date:	Fri, 21 Nov 2014 17:53:09 +0100
From:	David Herrmann <dh.herrmann@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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>,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: Re: kdbus: add node and filesystem implementation

Hi

On Fri, Nov 21, 2014 at 5:35 PM, Andy Lutomirski <luto@...capital.net> wrote:
> 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

Yes, we should add that. Nice catch!

> 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.

Buses show up as directories in kdbusfs. You can bind-mount them
anywhere you want and you will get access to the endpoints in there.

Thanks
David
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