On Wed, 2015-04-15 at 23:48 +0100, Al Viro wrote: > On Wed, Apr 15, 2015 at 03:28:58PM -0700, Andy Lutomirski wrote: > > On Wed, Apr 15, 2015 at 3:18 PM, Al Viro <v...@zeniv.linux.org.uk> wrote: > > > On Wed, Apr 15, 2015 at 03:11:17PM -0700, Andy Lutomirski wrote: > > > > > >> This is functionally identical to passing AF_UNIX socket fds over > > >> SCM_RIGHTS, but I want something much lighter weight. > > > > > > Most of the weight in SCM_RIGHTS comes from the fact that you can > > > pass AF_UNIX sockets over it, which requires a garbage collector. > > > Exclude that and suddenly it becomes very cheap... > > > > I should have been more specific. I don't mean the performance of > > SCM_RIGHTS itself; I mean the memory overhead of keeping tons of fds > > around, each with their socket data structures and buffers. > > > > I think that dbus could be quite efficiently implemented with a > > userspace daemon that just introduces peers to each other, but the fd > > explosion could be rather bad for some use cases. > > > > I'll be the first to admit that I don't have a clean API in mind. > > There was a lightweight fd proposal way back when, but it never went > > anywhere, and it might not be suitable anyway. > > Wait, are you talking about the overhead of descriptors used for capability > tokens (essentially zero - one system-wide struct file per capability + > one pointer in descriptor table of anyone who holds it + two bits in > bitmaps in the sam descriptor tables) or about the overhead of descriptors > used to send/receive those over? The latter don't have to be sockets > at all - they could bloody well be files on some ipcfs, or character device, > or FIFOs, etc.
This kind of remind me futex : From an apparent simple idea we got to the point of having more than 3000 lines of code in kernel/futex.c It is sad that af_unix was chosen to support fd passing in the first place. This is serious DOS vector. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
