Re: AF_BUS socket address family

On Fri, 29 Jun 2012 20:13:50 -0400
Benjamin LaHaise [off-list ref] wrote:

On Sat, Jun 30, 2012 at 12:42:30AM +0100, Vincent Sanders wrote:

quoted

The current users are suffering from the issues outlined in my
introductory mail all the time. These issues are caused by emulating an
IPC system over AF_UNIX in userspace.

Nothing in your introductory statements indicate how your requirements 
can't be met through a hybrid socket + shared memory solution.  The IPC 
facilities of the kernel are already quite rich, and sufficient for 
building many kinds of complex systems.  What's so different about DBus' 
requirements?

dbus wants to
- multicast
- pass file handles
- never lose an event
- be fast
- have a security model

The security model makes a shared memory hack impractical, the file
handle passing means at least some of it needs to be AF_UNIX. The event
loss handling/speed argue for putting it in kernel.

I'm not convinced AF_BUS entirely sorts this either. In particular the
failure case dbus currently has to handle for not losing events allows it
to identify who in a "group" has jammed the bus by not listening (eg by
locking up). This information appears to be lost in the AF_BUS case and
that's slightly catastrophic for error recovery.

Alan