On Thu, 13 Jul 2000, Phil Wilshire wrote:
Phil,
I hope you can comment on my comment on this post of yours...
> The zentropix package ( Yes I do work for them ) allows you to create a
> fifo from a user space program.
[...]
> > To make them easier to use, fifos can now be created by the user at
> > open time. If a fifo that does not exist already is opened, it is
> > created with a 1K buffer. Any following creation on modules side
> > resizes it without any loss of data. Again if you want to create a
> > fifo from the user side with a desired buffer size you can use: -
> > rtf_open_sized(const char *dev, perm, size).
... in combination with Victor Yodaiken's independent reply to the
original post, in which he (Victor) claims that the RTL approach is
``easier to use'' because it is clear and simple...
All depends on the definition of ``easier to use'' of course... My (very
non-authorative) ideas and questions about this issue:
- A `feature' like ``If a fifo that does not exist already is opened,
it is created with a 1K buffer'' carries IMHO the danger that is
found all over the place in so-called ``user friendly'' software:
the fact that the fifo does not exist already and the user tries to
access it nevertheless looks (to me at least) very much like a
programming error from the user, and ``hiding'' this error from the
user by not telling him and using a default _will_ give problems
later on (which will be _much_ more difficult to trace...).
- Moreover, the 1K default is another source of potential errors: for
example, a user writes a first program, using a fifo created by default
and the buffer size doesn't create problems _for that particular_
program. He thinks ``waw, nice feature, doesn't have to bother about
fifos ever again'', and the next time he writes another program
(needing much more than a 1K buffer!) and oops, program doesn't work
anymore...
- as a user the most ``user friendly'' thing I can imagine is _one single_
well defined and well documented and unambiguous way to work with a
given concept (i.c. fifos)... I don't know how this is solvable in
the RTL-RTAI world ;-) Through the ``common API'' initiative perhaps?
- is the fifo created from user space (by default or not) fully
compatible with the real time space view on this same fifo?
I mean: can any real time task work with this fifo without having to
know how it was created? Same question for a user space task.
(Sorry, but I didn't look at the details of all the fifo code in all
different packages...)
--
[EMAIL PROTECTED] (Ph.D.) Fax: +32-(0)16-32 29 87
Dept. Mechanical Eng., Div. PMA, Katholieke Universiteit Leuven, Belgium
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