MFC r333436: only launch getty if underlying device exists

Note: pc98 isn't run under VM, so I didn't do a direct commit to it.

Approved by: re@ (gjb@)

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Enable ttyu1, ttyu2, ttyu3 for arm installations.

This should make all consoles available, whether it
is VGA, HDMI, serial, or JTAG, but more importantly
enables all consoles when ttyu0 is not predictable.
For example, the Pandaboard ES apparently has three
consoles available, but the DB9/RS232 serial port is
ttyu2, so not available by default after the system
boots.

MFC after: 3 days
Sponsored by: The FreeBSD Foundation

Merge ^/projects/release-arm-redux into ^/head.

Of note:

- This commit adds native FreeBSD/arm release build support without
requiring out-of-tree utilities.

- Part of this merge removes the WANDBOARD-{SOLO,DUAL,QUAD} kernel
configuration files, for which the IMX6 kernel configuration file
should be used instead.

- The resulting images have a 'freebsd' user (password 'freebsd'),
to allow ssh(1) access when console access is not available (VGA
or serial). The default 'root' user password is set to 'root'.

- The /etc/ttys file for arm images now enable both ttyv0 and ttyu0
by default.

Help from: many (boot testing, feedback, etc.)
Sponsored by: The FreeBSD Foundation

Change the terminal type/class for enabled serial lines to 3wire. This
allows us to change the uart(4) driver to not hardcode specific line
settings for the serial console.

A terminal type of 3wire makes sure the console still works when no DCD
signal is present, which preserves behviour. When it is known that the
terminal server (or DCE in general) provides DCD, a terminal type/class
of std can be used. This has the effect of being logged out when one
disconnects from the console -- improving security overall.

Likewise, when uart(4) does not fixate the baudrate, one can change
the terminal type/class to set a specific baudrate. An operator can use
this to change the console speed mid-flight, without needing a reboot.
Of course it helps in this respect if and when the firmware can be
configured from the OS.

The above mentioned capabilities depend on uart(4) being changed, which
is to happen next.

Remove the reference to pseudo-terminals from the description.

Pseudo-terminals are no longer listed in this file, since the utmpx
implementation doesn't depend on ttyslot().

Remove pseudo-terminals from ttys(5).

When we had utmp(5), we had to list all the psuedo-terminals in ttys(5)
to make ttyslot(3) function properly. Now that pututxline(3) deals with
slot allocation internally (not based on TTY names), we don't need to
list all the TTYs on the system in ttys(5) to make user accounting work
properly.

This patch removes all the entries from the /etc/ttys files, but also
the pts(4) entries that were appended implicitly, which was added in
r154838.

Switch the default terminal emulation style to xterm for most platforms.

Right now syscons(4) uses a cons25-style terminal emulator. The
disadvantages of that are:

- Little compatibility with embedded devices with serial interfaces.
- Bad bandwidth efficiency, mainly because of the lack of scrolling
regions.
- A very hard transition path to support for modern character sets like
UTF-8.

Our terminal emulation library, libteken, has been supporting
xterm-style terminal emulation for months, so flip the switch and make
everyone use an xterm-style console driver.

I still have to enable this on i386. Right now pc98 and i386 share the
same /etc/ttys file. I'm not going to switch pc98, because it uses its
own Kanji-capable cons25 emulator.

IMPORTANT: What to do if things go wrong (i.e. graphical artifacts):

- Run the application inside script(1), try to reduce the problem and
send me the log file.
- In the mean time, you can run `vidcontrol -T cons25' and `export
TERM=cons25' so you can run applications the same way you did before.
You can also build your kernel with `options TEKEN_CONS25' to make all
virtual terminals use the cons25 emulator by default.

Discussed on: current@

Remove the note about using vt220, which makes no sense at all.

vt220 will not work better. Even though it probably will remove warnings
about unknown terminal types, a cons25 emulator is not compatible with
vt220 at all.

Remove pts(4) entries from /etc/ttys.

Even though I increased the amount of pts(4) entries in /etc/ttys some
time ago, I didn't realize back then those entries shouldn't have been
there in the first place.

I just looked at the getttyent() source code and it turns out when you
call setttyent(), it walks through /dev/pts and looks for the device
with the highest number. After you receive EOF's from getttyent(), it
makes up entries for pts(4) devices.

This means that adding entries for pts(4) is somewhat harmful, because
if you now traverse the list, you get redundant entries, so just remove
them.

turn off ttyv*; not aware of any arm-based systems with syscons

Reviewed by: imp

Restore 256 pty(4) entries.

As discussed with Robert Watson on the src-committers list, it is safer
to keep at least some pty(4) entries in /etc/ttys, for applications that
roll their own PTY allocation routine and only search for BSD-style
PTY's.

This means we've now just toggled the amount of entries for pts(4) and
pty(4).

Requested by: rwatson

Remove old BSD-style entries from /etc/ttys and increase pts(4) to 512.

Because we now use pts(4)-style PTY's exclusively, there is no use for
these entries in /etc/ttys. Right now the pts(4) entries only go from 0
to 255. Because we're going to touch these files anyway, increase the
number to 511.

Discussed with: philip (ex-mentor)

Bump up the number of ttys supported by pty(4) to 512 by making use of
[pt]ty[lmnoLMNO][0-9a-v].

MFC after: 3 days
Reviewed by: rwatson

Add ttys lines for pts/0-pts/255.

MFC after: 3 days

Use ttyu instead of ttyd for arm, since we will probably never use sio(4).

Approved by: re (blanket)

Remove more vestiges of /usr/X11R6, but leave mtree for portmgr.

Add ttyu0 as a serial console, as we're using the uart(4) driver on arm.

Import the ttys file for arm.
make TARGET_ARCH=arm world now works (but still with external patches for
the toolchain bits).