On Wed, Oct 29, 2014 at 4:40 PM, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Thu, Oct 30, 2014 at 12:24:02AM +0100, Jiri Kosina wrote: >> On Wed, 29 Oct 2014, Greg Kroah-Hartman wrote: >> >> > > > kdbus is a kernel-level IPC implementation that aims for resemblance to >> > > > the the protocol layer with the existing userspace D-Bus daemon while >> > > > enabling some features that couldn't be implemented before in userspace. >> > > >> > > I'd be interested in the features that can't be implemented in userspace >> > > (and therefore would justify existence of kdbus in the kernel). Could you >> > > please point me to such list / documentation? >> > >> > Lennart has given whole talks about this in the past, here's a recent >> > talk going into the details: >> > https://www.youtube.com/watch?v=HPbQzm_iz_k >> >> I think it's a reasonable expectation that kernel patch submissions should >> be reasonably self-contained though. We've always been very strict about >> pushing everybody to provide extensive cover letters, changelogs and >> explanations, so this shouldn't really be an exception, I think. > > There is a 1815 line documentation file in this series, so we aren't > trying to not provide this type of information here at all. But yes, > more background, about why this can't be done in userspace (zero copy, > less context switches, proper credential passing, timestamping, availble > at early-boot, LSM hooks for security models to tie into, race-free > interfaces, container/namespace support, etc.) should be added to the > docs as well. It's worth noting that: - Proper credential passing could be added to UNIX sockets, and we may want to do that anyway. Also, the current kdbus semantics seem to be "spew lots of credentials and other miscellaneous potentially-sensitive and sometime spoofable information all over the place", which isn't obviously an improvement. (This is fixable, but it will almost certainly not be compatible with current systemd kdbus code if fixed.) - The current kdbus patches seem to be worse than UNIX sockets from a namespace perspective, but maybe I'm misunderstanding how it's supposed to work. UNIX sockets work quite nicely in containers. - There's an obvious interface to add timestamping to UNIX sockets (it could work exactly the way it does for UDP / PTP). - I'm unconvinced by this performance argument without numbers. The kdbus credential code, at least, looks to be quite heavy on allocation and atomics. This isn't to say that the current userspace D-Bus daemon doesn't also serialize everything, but it could be made multithreaded. - Race-free? What are the races that are inherent to UNIX sockets? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
