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)
[off-list ref] wrote:

quoted

On 01/26/2015 04:26 PM, Tom Gundersen wrote:

quoted

On Mon, Jan 26, 2015 at 3:42 PM, Michael Kerrisk (man-pages)
[off-list ref] wrote:

quoted

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/