linux-kernel - Re: [GIT PULL] kdbus for 4.1-rc1

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Message-ID: <CALCETrVSsyUUNujCi+oYTBcy+6ROahem4M0A2axCivRwrA4myw@mail.gmail.com>
Date:	Wed, 15 Apr 2015 15:28:58 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Richard Weinberger <richard.weinberger@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>, Tom Gundersen <teg@...m.no>,
	Jiri Kosina <jkosina@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1

On Wed, Apr 15, 2015 at 3:18 PM, Al Viro <viro@...iv.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.

--Andy
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