MPSAFE TTY schedule

Hello everyone,

About 2 weeks ago I sent a message to these lists about the new MPSAFE
TTY layer I've been working on. In my opinion, it is quite robust and
after some minor polishing it should be a great candidate for inclusion
in FreeBSD -CURRENT (never to be MFC'd). The last 2 weeks I've ported
all the console drivers and fixed some bugs after I received some
feedback from testers.

Below is a list of pros and cons of the new TTY layer:

+ The new TTY layer allows drivers to operate without the Giant lock.
  Drivers like uart(4), the console drivers and the pseudo-terminal
  driver already support fine grained locking.

+ The new pseudo-terminal driver is capable of garbage collecting unused
  PTY's. Because PTY's are never recycled, they are a lot more robust
  (they are always initialized the same, no need to revoke() them before
  usage, etc).

+ The new TTY layer includes a new buffer scheme called the ttyinq and
  ttyoutq. Unlike clists, they provide unbuffered copying of data back
  to userspace, making read() calls in raw mode more efficient.

+ The programming interface for kernel drivers is a lot more simple.
  There is no need to have any knowledge about the internal state
  of the TTY layer.

- Not all drivers have been ported to the new TTY layer yet. These
  drivers still need to be ported: sio(4), cy(4), digi(4), ubser(4),
  uftdi(4), nmdm(4), ng_h4(4), ng_tty(4), snp(4), rp(4), rc(4), si(4),
  umodem(4), dcons(4).

Even though drivers are very important to have, I am convinced we can
get these working not long after the code as been integrated. I have
considered adding two TTY layers to the FreeBSD kernel, but looking at
the drivers, I'm not sure this is worth it, it turns certain parts of
the kernel into rubbish. If you really care about one of these drivers,
please port it to the new TTY layer as soon as possible!

Below is the schedule I'm proposing for the integration of the MPSAFE
TTY layer into our kernel. I would really appreciate it if I could get
this code in before the end of the summer break, because I've got heaps
of spare time to fix any problems then.

July 2 2008 (today):
	Send a schedule to the lists about the integration of the MPSAFE
	TTY layer.

July 13 2008:
	Make uart(4) the default serial port driver, instead of sio(4).
	sio(4) has not been ported to the new TTY layer and is very hard
	to do so. uart(4) has been proven to be more portable than
	sio(4) and already supports the hardware we need.

July 20 2008:
	Send another heads-up to the lists about the new TTY layer.
	Kindly ask people to test the patchset, port more drivers, etc.

August 3 2008:
	Disconnect drivers from the build that haven't been patched in
	the MPSAFE TTY branch.

August 8 2008:
	Send the last heads-up to the lists, to warn people about the
	big commit.

August 10 2008:
	Commit the new MPSAFE TTY driver in several commits (first
	commit the layer itself, then commit changes to drivers one by
	one).

I'll stay close to my inbox the next couple of days after I've
integrated the code, to make sure I can fix any bugs which may be
spotted to be fixed shortly.

Please, make sure we can make this a smooth transition by
testing/reviewing my code. I tend to generate diffs very often. They can
be downloaded here:

	http://www.il.fontys.nl/~ed/projects/mpsafetty/patches/

Thanks!

-- 
 Ed Schouten <ed_at_80386.nl>
 WWW: http://80386.nl/