Rework tty_drain() to poll the hardware for completion, and restore
drain timeout handling to historical freebsd behavior.

The primary reason for these changes is the need to have tty_drain() call
t

Rework tty_drain() to poll the hardware for completion, and restore
drain timeout handling to historical freebsd behavior.

The primary reason for these changes is the need to have tty_drain() call
ttydevsw_busy() at some reasonable sub-second rate, to poll hardware that
doesn't signal an interrupt when the transmit shift register becomes empty
(which includes virtually all USB serial hardware). Such hardware hangs
in a ttyout wait, because it never gets an opportunity to trigger a wakeup
from the sleep in tty_drain() by calling ttydisc_getc() again, after
handing the last of the buffered data to the hardware.

While researching the history of changes to tty_drain() I stumbled across
some email describing the historical BSD behavior of tcdrain() and close()
on serial ports, and the ability of comcontrol(1) to control timeout
behavior. Using that and some advice from Bruce Evans as a guide, I've
put together these changes to implement the hardware polling and restore
the historical timeout behaviors...

- tty_drain() now calls ttydevsw_busy() in a loop at 10 Hz to accomodate
hardware that requires polling for busy state.

- The "new historical" behavior for draining during close(2) is retained:
the drain timeout is "1 second without making any progress". When the
1-second timeout expires, if the count of bytes remaining in the tty
layer buffer is smaller than last time, the timeout is extended for
another second. Unfortunately, the same logic cannot be extended all
the way down to the hardware, because the interface to that layer is a
simple busy/not-busy indication.

- Due to the previous point, an application that needs a guarantee that
all data has been transmitted must use TIOCDRAIN/tcdrain(3) before
calling close(2).

- The historical behavior of honoring the drainwait setting for TIOCDRAIN
(used by tcdrain(3)) is restored.

- The historical kern.drainwait sysctl to control the global default
drainwait time is restored, but is now named kern.tty_drainwait.

- The historical default drainwait timeout of 300 seconds is restored.

- Handling of TIOCGDRAINWAIT and TIOCSDRAINWAIT ioctls is restored
(this also makes the comcontrol(1) drainwait verb work again).

- Manpages are updated to document these behaviors.

Reviewed by: bde (prior version)

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sys/kern: spelling fixes in comments.

No functional change.

MfH @r295202

Expect to see panics in routing code at least now.

Merge ^/head r294777 through r294960.

MFH

Sponsored by: The FreeBSD Foundation

Don't clear the software flow control flag before draining for last
close or assert the bug that it is clear when leaving.

Remove an unrelated rotted comment that was attached to the buggy
clearing.

Don't clear the software flow control flag before draining for last
close or assert the bug that it is clear when leaving.

Remove an unrelated rotted comment that was attached to the buggy
clearing.

Since draining is not done in more cases, flushing is needed in more
cases, so start fixing flushing:
- do a full flush in ttydisc_close(). State what POSIX requires more
clearly. This was missing ttydevsw_pktnotify() calls to tell the
devsw layer to flush. Hardware tty drivers don't actually flush
since they don't understand this API.
- fix 2 missing wakeups in tty_flush(). Most of the wakeups here are
unnecessary for last close. But ttydisc_close() did one of the
missing ones.

This flow control bug ameliorated the design bug of requiring
potentially unbounded waits in draining. Software flow control is the
easiest way to get an unbounded wait, and a long wait is sometimes
actually useful. Users can type the xoff character on the receiver
and (if ixon is set on the sender) expect the output to be held until
the user is ready for more.

Hardware flow control can also give the unbounded wait, and this bug
didn't affect hardware flow control. Unbounded waits from hardware
flow control take a more unusual configuration. E.g., a terminal
program that controls the modem status lines, or unplugging the cable
in a configuration where this doesn't break the connection.

The design bug is still ameliorated by a newer bug in draining for
last close -- the 1 second timeout. E.g., if the user types the
xoff character and the sender reaches last close, then output is
not resumed and the wait times out after just 1 second. This is
broken, but preferable to an unbounded wait. Before this change,
the output was resumed immediately and usually completed.

Submitted by: bde
MFC after: 2 weeks

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Restore flushing of output for revoke(2) again. Document revoke()'s
intended behaviour in its man page. Simplify tty_drain() to match.
Don't call ttydevsw methods in tty_flush() if the device is go

Restore flushing of output for revoke(2) again. Document revoke()'s
intended behaviour in its man page. Simplify tty_drain() to match.
Don't call ttydevsw methods in tty_flush() if the device is gone
since we now sometimes call it then.

The flushing was supposed to be implemented by passing the FNONBLOCK
flag to VOP_CLOSE() for revoke(). The tty driver is one of the few
that can block in close and was one of the fewer that knew about this.

This almost worked in FreeBSD-1 and similarly in Net/2. These
versions only almost worked because there was and is considerable
confusion between IO_NDELAY and FNONBLOCK (aka O_NONBLOCK). IO_NDELAY
is only valid for VOP_READ() and VOP_WRITE(). For other VOPs it has
the same value as O_SHLOCK. But since vfs_subr.c and tty.c
consistently used the wrong flag and the O_SHLOCK flag is rarely set,
this mostly worked. It also gave the feature than applications could
get the non-blocking close by abusing O_SHLOCK.

This was first broken then fixed in 1995. I changed only the tty
driver to use FNONBLOCK, as a hack to get non-blocking via the normal
flag FNONBLOCK for last closes. I didn't know about revoke()'s use
of IO_NDELAY or change it to be consistent, so revoke() was broken.
Then I changed revoke() to match.

This was next broken in 1997 then fixed in 1998. Importing Lite2 made
the flags inconsistent again by undoing the fix only in vfs_subr.c.

This was next broken in 2008 by replacing everything in tty.c and not
checking any flags in last close. Other bugs in draining limited the
resulting unbounded waits to drain in some cases.

It is now possible to fix this better using the new FREVOKE flag.
Just restore flushing for revoke() for now. Don't restore or undo any
hacks for ordinary last closes yet. But remove dead code in the
1-second relative timeout (r272789). This did extra work to extend
the buggy draining for revoke() for as long as possible. The 1-second
timeout made this not very long by usually flushing after 1 second.

Submitted by: bde
MFC after: 2 weeks

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Merge ^/head r294599 through r294776.

- Make the code consistent with itself style-wise and bring it closer
to style(9).
- Mark unused arguments as such.
- Make the ttystates table const.

Don't allow opening the callout device when the callin device is already
open (in disguise as the console device). The only allowed combination
was supposed to be the callin device with the console.

Don't allow opening the callout device when the callin device is already
open (in disguise as the console device). The only allowed combination
was supposed to be the callin device with the console.

Fix the assertion in ttydev_close() that was meant to detect this (it
only detected all 3 devices being open). Assert this in ttydev_open()
too.

Submitted by: bde
MFC after: 2 weeks

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Fix the %b flags string for ddb. All bits above the 5th
(TF_OPENED_CONS) were broken in r188147 by adding TF_OPENED_CONS
without updating the string. It was especially confusing to display
OPENED_C

Fix the %b flags string for ddb. All bits above the 5th
(TF_OPENED_CONS) were broken in r188147 by adding TF_OPENED_CONS
without updating the string. It was especially confusing to display
OPENED_CONS as GONE and BYPASS as ZOMBIE. 2 flags at the end were
not updated in r188487.

Don't print an extra 0x prefix for %p in a ddb command. In the rest
of the kernel there are more than 6000 lines with %p and only about
40 with this bug.

Print a non-extra 0x prefix for %b in a ddb command. In the rest
of the kernel, there are approx. 180 lines with %b and 2/3 of them
have this bug.

Submitted by: bde
MFC after: 2 weeks

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MFH

Sponsored by: The FreeBSD Foundation

Merge ^/head r294169 through r294598.

In tty_dealloc(), clear the queues. See the comment for a scenario
which explains why ttydev_leave() cleanup might not happen.

Submitted by: bde
MFC after: 3 weeks

MFH @r294567

MFH

Sponsored by: The FreeBSD Foundation

Fix tty_drain() and, thus, TIOCDRAIN of the current tty(4) incarnation
to actually wait until the TX FIFOs of UARTs have be drained before
returning. This is done by bringing the equivalent of the TS

Fix tty_drain() and, thus, TIOCDRAIN of the current tty(4) incarnation
to actually wait until the TX FIFOs of UARTs have be drained before
returning. This is done by bringing the equivalent of the TS_BUSY flag
found in the previous implementation back in an ABI-preserving way.
Reported and tested by: Patrick Powell

Most likely, drivers for USB-serial-adapters likewise incorporating
TX FIFOs as well as other terminal devices that buffer output in some
form should also provide implementations of tsw_busy.

MFC after: 3 days

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MFH

Sponsored by: The FreeBSD Foundation

Merge ^/head r293280 through r293429.

Convert tty common code to use make_dev_s().

Tty.c was untypical in that it handled the si_drv1 issue consistently
and correctly, by always checking for si_drv1 being non-NULL and
sleeping if NULL.

Convert tty common code to use make_dev_s().

Tty.c was untypical in that it handled the si_drv1 issue consistently
and correctly, by always checking for si_drv1 being non-NULL and
sleeping if NULL. The removed code also illustrated unneeded
complications in drivers which are eliminated by the use of new KPI.

Reviewed by: hps, jhb
Discussed with: bde
Sponsored by: The FreeBSD Foundation
MFC after: 3 weeks
Differential revision: https://reviews.freebsd.org/D4746

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Merge sync of head

Merge from head

Merge r278538 through r279514.

Merging ^/head r278916 through r279022.

MFH: r278593-r278966

Sponsored by: The FreeBSD Foundation