Re: [Xenomai-help] xn_pipe_create [minor]

[Philippe Gerum <rpm@xenomai.org>]

Ignacio García Pérez wrote:
> Dmitry Adamushko wrote:
> 
> 
>>xenomai-help-bounces@domain.hid wrote on 14.11.2005 13:15:07:
>>
>>
>>>Hi,
>>>
>>>The registry system is great, allows to forget about agreeing about an
>>>arbitrary minor number for pipes. But as far as I ca see, you still have
>>>to pass an unique "minor" number to rt_pipe_create.
>>>
>>>What if you have several rt modules?... you must make sure you assign
>>>different minor numbers to each pipe!.
>>>
>>>Wouldn't be useful to have a way to let the rt_pipe_create decide which
>>>minor to use? (a free one, of course)
>>
>>It can be done and that would work if both sides of the communication
>>channel are real-time threads so a rt_pipe_create/bind() pair may be
>>used to establish a connection.
>>
>>But what should be done if another side is a linux task and uses a
>>mere open() call?
>>
>>Currently, a naming convention is a "/dev/rtpN", N - is a minor being
>>used by rt_pipe_create() and both sides of the channel must be aware
>>of it.
>>
>>Moreover, a client side of the connection may be open even in case
>>there is no server side yet (the one that calls rt_pipe_create) at the
>>mement. In that case, the client is blocked in open().
>>
>>So the only convention between both sides can be a minor number +
>>pre-created /dev/rtp[0, OPT_PIPE_NRDEV] character devices.
>>
> 
> Um... I think you are wrong. When the rt task creates a pipe, a symbolik
> link appears at /proc/xenomai/registry/pipes. Its name is the fifo name,
> and points to the /dev/rtpN device. That's what I was talking about when
> I said "clever procfs usage of xenomai".
> 
> Using this scheme, user mode programs just need to open()
> /proc/xenomai/registry/pipes/whatever to access a named pipe, without
> having to know the minor number.
> 
> Under these circumstances, it would be *very* useful to have
> rt_pipe_create choose an unused minor automagically (for example passing
> -1 as the minor).
>

Sounds reasonable.

> Currently, I'm emulating this by calling rt_pipe_create for minor =
> 0,1,2... until it succeeds or returns any error different than -EBUSY.
> 
> Nacho.
> 
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-- 

Philippe.