| > Consider audio instead. OSS always provided pretty much all the hardware features, but allow no resource sharing. Every single evolution on that front has been an increase in complexity to allow for resource sharing. This is not true. Early evolution of ALSA included lots of work on handling high channel count, memory-mapped devices (and their opposite, a few devices around in about 2000 that require active CPU involvement in data transfer). At some point, more evolution was required to deal with asynchronous interfaces like the USB ones that are now ubiquitous. The Intel HDA "specification" created a huge amount of work to model the topologically indistinct hardware mixers that it allowed. It remains the case that ALSA provides no facilities for resource sharing that are used by more than a handful of obstinate folk, so there has been essentially no evolution within ALSA itself toward that goal (see next para). > And it's interesting because the effort went in and out of the kernel a couple of times. Once OSS was dropped, the only resource sharing left on the kernel side in ALSA was the dmix layer. That continues to exist today, but has never worked reliably, which is part of the reason why PulseAudio came into existence. > Describing the evolution of OSS/ALSA in linux/freebsd would be too long, however we now have very fat daemons sitting in front of the HW just for resource sharing. I object to JACK being called "a very fat daemon". It's lean and mean and fairly clean (even the version I didn't write). Perhaps you mean PulseAudio, but that does much, much more than just "resource sharing". As a side-note, Apple did move resource sharing out of the kernel. At some point that was all kernel-side, and at some point, coreaudiod showed up as a user-space daemon that was eventually clearly doing the same thing. |