Re: MIDI+USB - one way?

[Takashi Iwai <tiwai@suse.de>]

At Mon, 05 Aug 2002 12:40:19 +0200,
Clemens Ladisch wrote:
> 
> To quote one of the standards (I think IEEE 1003.1 is POSIX)
> <http://www.opengroup.org/onlinepubs/007904975/functions/read.html>:
> | When attempting to read a file (other than a pipe or FIFO) that
> | supports non-blocking reads and has no data currently available:
> |
> | If O_NONBLOCK is set, read() shall return -1 and set errno to [EAGAIN].
> |
> | If O_NONBLOCK is clear, read() shall block the calling thread until
> | some data becomes available.
> |
> | The use of the O_NONBLOCK flag has no effect if there is some data
> | available.
> | [...]
> | Upon successful completion, where nbyte is greater than 0, read()
> | (...) shall return the number of bytes read. This number shall never
> | be greater than nbyte. The value returned may be less than nbyte if
> | (...) the file is a (...) special file and has fewer than nbyte bytes
> | immediately available for reading. For example, a read() from a file
> | associated with a terminal may return one typed line of data.

ok, it's clearly mentioned here.
then we should fix this behavior.


> 
> > (and i believe that no applications suffer by this change.)
> 
> Yes, because applications expect the OSS behaviour.
> 
> I didn't really look at the OSS PCM read() implementation, but the
> sequencer read() already implements the correct POSIX behaviour.

i don't think that the oss pcm interface ever suffices the definition
of posix above.  but we cannot change it since most of applications
assume that the read aligned in a block size.

in the case of alsa, this low-level behavior can be changed, because
the difference can be absorbed inside the alsa-lib.  but i see no good
reason to change this now.


Takashi


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