Message-ID: <54C7D0A3.4000900@gmail.com>
Date:	Tue, 27 Jan 2015 18:53:39 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	David Herrmann <dh.herrmann@...il.com>
CC:	mtk.manpages@...il.com, Tom Gundersen <teg@...m.no>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>, Arnd Bergmann <arnd@...db.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jiri Kosina <jkosina@...e.cz>,
	Andy Lutomirski <luto@...capital.net>,
	Linux API <linux-api@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Johannes Stezenbach <js@...21.net>,
	Theodore T'so <tytso@....edu>,
	christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 01/13] kdbus: add documentation

On 01/27/2015 04:23 PM, David Herrmann wrote:
> Hi
> 
> On Mon, Jan 26, 2015 at 5:45 PM, Michael Kerrisk (man-pages)
> <mtk.manpages@...il.com> wrote:
>> On 01/26/2015 04:26 PM, Tom Gundersen wrote:
>>> On Mon, Jan 26, 2015 at 3:42 PM, Michael Kerrisk (man-pages)
>>> <mtk.manpages@...il.com> wrote:
>>>> 2. Is the API to be invoked directly by applications or is intended to
>>>>    be used only behind specific libraries? You seem to be saying that
>>>>    the latter is the case (here, I'm referring to your comment above
>>>>    about sd-bus). However, when I asked David Herrmann a similar
>>>>    question I got this responser:
>>>>
>>>>       "kdbus is in no way bound to systemd. There are ongoing efforts
>>>>        to port glib and qt to kdbus natively. The API is pretty simple
>>>>        and I don't see how a libkdbus would simplify things. In fact,
>>>>        even our tests only have slim wrappers around the ioctls to
>>>>        simplify error-handling in test-scenarios."
>>>>
>>>>    To me, that implies that users will employ the raw kernel API.
>>>
>>> The way I read this is that there will (probably) be a handful of
>>> users, namely the existing dbus libraries: libdus, sd-bus, glib, Qt,
>>> ell, and maybe a few others. However, third-party developers will not
>>> know/care about the details of kdbus, they'll just be coding against
>>> the dbus libraries as before (might be minor changes, but they
>>> certainly won't need to know anything about the kernel API). Similarly
>>> to how userspace developers now code against their libc of choice,
>>> rather than use kernel syscalls directly.
>>
>> Thanks, Tom, for the input. I'm still confused though, since elsewhere
>> in this thread David Herrmann said in response to a question of mine:
>>
>>     I think we can agree that we want it to be generically useful,
>>     like other ipc mechanisms, including UDS and netlink.
>>
>> Again, that sounds to me like the vision is not "a handful of users".
>> Hopefully Greg and David can clarify.
> 
> I only expect a handful of users to call the ioctls directly. The
> libraries that implement the payload-marshaling, in particular. It's a
> similar situation with netlink.

Thanks, David, for the clarification. I think it would have been helpful
to have that more clearly stated up front, especially as some comments 
in this thread, such as the above, could be interpreted to mean quite 
the opposite. Can I suggest that some text on this point be added to 
kdbus.txt?

Thanks,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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