kern: tty: recanonicalize the buffer on ICANON/VEOF/VEOL changes

Before this change, we would canonicalize any partial input if the new
local mode is not ICANON, but that's about it. If we were switching
from -ICANON -> ICANON, or if VEOF/VEOL changes, then our internal canon
accounting would be wrong.

The main consequence of this is that in ICANON mode, we would
potentially hang a read(2) longer if the new VEOF/VEOL appears later in
the buffer, and FIONREAD would be similarly wrong as a result.

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D43456

kern: tty: fix EOF handling for canonical reads

If the read(2) buffer is one byte short of an EOF, then we'll end up
reading the line into the buffer, then re-entering and seeing an EOF at
the beginning of the inq, assuming it's a zero-length line.

Fix this corner-case by searching one more byte than we have available
for an EOF. If we found it, then we'll trim it here; otherwise, we'll
limit our read to just the space we have in the out buffer and the next
read(2) will (potentially) read the remainder of the line.

Fix FIONREAD while we're here to match what an application can expect
read(2) to return -- scan for the first break character in the part of
the input that's been canonicalized, we'll never return more than that.

PR: 276220
Reviewed by: cy, imp (both previous version), kib
Differential Revision: https://reviews.freebsd.org/D43378

sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

tty: convert tty_lock_assert to tty_assert_locked to hide lock type

A later change, currently being iterated on in D24459, will in-fact change
the lock type to an sx so that TTY drivers can sleep on it if they need to.
Committing this ahead of time to make the review in question a little more
palatable.

tty_lock_assert() is unfortunately still needed for now in two places to
make sure that the tty lock has not been recursed upon, for those scenarios
where it's supplied by the TTY driver and possibly a mutex that is allowed
to recurse.

Suggested by: markj

sys/sys: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Add ttydisc_rint_simple().

I noticed several drivers in our tree don't actually care about parity
and framing, such as pts(4), snp(4) (and my partially finished console
driver). Instead of duplicating a lot of code, I think we'd better add a
utility function for those drivers to quickly process a buffer of input.

Also change pts(4) and snp(4) to use this function.

- Import the HEAD csup code which is the basis for the cvsmode work.

Introduce a hooks layer for the MPSAFE TTY layer.

One of the features that prevented us from fixing some of the TTY
consumers to work once again, was an interface that allowed consumers to
do the following:

- `Sniff' incoming data, which is used by the snp(4) driver.

- Take direct control of the input and output paths of a TTY, which is
used by ng_tty(4), ppp(4), sl(4), etc.

There's no practical advantage in committing a hooks layer without
having any consumers. In P4 there is a preliminary port of snp(4) and
thompsa@ is busy porting ng_tty(4) to this interface. I already want to
have it in the tree, because this may stimulate others to work on the
remaining modules.

Discussed with: thompsa
Obtained from: //depot/projects/mpsafetty/...

Fix style(9) issue in TTY header files: document function argument names.

According to style(9), function argument names should only be omitted
for prototypes that are exported to userspace. This means we should
document the function arguments in the TTY header files, because they
are only used in userspace.

While there, change the type of the buffer argument of
ttydisc_rint_bypass() to `const void *' instead of `char *'.

Requested by: attilio
Obtained from: //depot/projects/mpsafetty/...

Small consistency bug: remove named function attribute.

Everywhere in <sys/ttydisc.h> we don't specify a function argument name,
except in a single place. Also remove it there.

Restore assertion that was removed in r182444.

While merging back my changes from Perforce, it seemed I removed a
locking assertion that still applies to ttydisc_rint_poll(). Restore it,
because it may come in handy.

Backport two small fixes from the MPSAFE TTY branch in Perforce:

- Implement IMAXBEL. It turned out the IMAXBEL termios switch was marked
as supported, while it had not been implemented.

- Don't go into the high watermark when in canonical mode, no data has
been canonicalized and the input buffer is full. This caused the
terminal to lock up. This prevented users from pressing
backspace/^U/etc in such cases.

This could easily be simulated by pasting a very big amount of data in
a shell with sh(1) in canonical mode.

Obtained from: //depot/projects/mpsafetty/...

Integrate the new MPSAFE TTY layer to the FreeBSD operating system.

The last half year I've been working on a replacement TTY layer for the
FreeBSD kernel. The new TTY layer was designed to improve the following:

- Improved driver model:

The old TTY layer has a driver model that is not abstract enough to
make it friendly to use. A good example is the output path, where the
device drivers directly access the output buffers. This means that an
in-kernel PPP implementation must always convert network buffers into
TTY buffers.

If a PPP implementation would be built on top of the new TTY layer
(still needs a hooks layer, though), it would allow the PPP
implementation to directly hand the data to the TTY driver.

- Improved hotplugging:

With the old TTY layer, it isn't entirely safe to destroy TTY's from
the system. This implementation has a two-step destructing design,
where the driver first abandons the TTY. After all threads have left
the TTY, the TTY layer calls a routine in the driver, which can be
used to free resources (unit numbers, etc).

The pts(4) driver also implements this feature, which means
posix_openpt() will now return PTY's that are created on the fly.

- Improved performance:

One of the major improvements is the per-TTY mutex, which is expected
to improve scalability when compared to the old Giant locking.
Another change is the unbuffered copying to userspace, which is both
used on TTY device nodes and PTY masters.

Upgrading should be quite straightforward. Unlike previous versions,
existing kernel configuration files do not need to be changed, except
when they reference device drivers that are listed in UPDATING.

Obtained from: //depot/projects/mpsafetty/...
Approved by: philip (ex-mentor)
Discussed: on the lists, at BSDCan, at the DevSummit
Sponsored by: Snow B.V., the Netherlands
dcons(4) fixed by: kan