Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Correct SIGTTIN handling.

In the old TTY layer, SIGTTIN was correctly handled like this:

while (data should be read) {
send SIGTTIN if not foreground process group
read data
}

In the new TTY layer, however, this behaviour was changed, based on a
false interpretation of the standard:

send SIGTTIN if not foreground process group
while (data should be read) {
read data
}

Correct this by pushing tty_wait_background() into the ttydisc_read_*()
functions.

Reported by: koitsu
PR: kern/173010
MFC after: 2 weeks

Fix faulty error code handling in read(2) on TTYs.

When performing a non-blocking read(2), on a TTY while no data is
available, we should return EAGAIN. But if there's a modem disconnect,
we should return 0. Right now we only return 0 when doing a blocking
read, which is wrong.

MFC after: 1 month

Fix found places where uio_resid is truncated to int.

Add the sysctl debug.iosize_max_clamp, enabled by default. Setting the
sysctl to zero allows to perform the SSIZE_MAX-sized i/o requests from
the usermode.

Discussed with: bde, das (previous versions)
MFC after: 1 month

Fix whitespace inconsistencies in TTY code.

Fix whitespace inconsistencies in the TTY layer and its drivers owned by me.

Print backspaces after echoing an EOF.

Applications like shells expect EOF to give no graphical output, while
our implementation prints ^D by default (tunable with stty echoctl).
Make the new implementation behave like the old TTY code. Print two
backspaces afterwards.

Reported by: koitsu
MFC after: 1 month

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.

Fix two bugs related to TTY input:

- fix write() on pseudo-terminal masters to return the amount of bytes
passed to the TTY, not the amount of bytes read from user.

- fix ttydisc_rint_bypass() to set the high watermark when it cannot
write all input, just like ttydisc_rint() itself.

Approved by: re (kib)

If we have a regular rint handler, never go into rint_bypass mode.

It turns out if we called cfmakeraw() on a TTY with only a rint handler
in place, it could inject data into the TTY, even though it should be
redirected. Always take a look at the hooks before looking at the
termios flags.

Use unsigned longs for the TTY's sysctl stats.

Spotted by: clang

Don't forget to relock the TTY after uiomove() returns an error.

Peter Holm just discovered this funny bug inside the TTY code: if
uiomove() in ttydisc_write() returns an error, we forget to relock the
TTY before jumping out of ttydisc_write(). Fix it by placing
tty_unlock() and tty_lock() around uiomove().

Submitted by: pho

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/...

Make sure the TTY has not disappeared out from under us before calling
ttydevsw_outwakeup(). This should fix panics which occur after remote
login sessions timeout during moderate TTY activity. An example of
where this might occur is where a pending write to the terminal is
occurring while sshd(8) is shutting down the TTY after a TCP timeout.

Submitted by: ed

Use size_t to store the return value of ttydisc_getc().

The ttydisc_getc() routine obtains a read length from ttyoutq_read().
For no valid reason, the current code stores this value in an int, and
returns a size_t. There is no need to perform this useless conversion.

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

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