Re: kdbus: add node and filesystem implementation

From: Andy Lutomirski
Date: Fri Nov 21 2014 - 11:35:40 EST

On Thu, Nov 20, 2014 at 9:02 PM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> From: Daniel Mack <daniel@xxxxxxxxxx>
> 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@xxxxxxxxxx>
> Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxx>
> Signed-off-by: Djalal Harouni <tixxdz@xxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---

> +
> +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.

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