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

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.

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s/timer_t/int/g

Remove itimers_event_hook, now it is a private function in kern_time.c.

Let itimer store itimerspec instead of itimerval, so I don't have to
convert to or from timeval frequently.

Introduce function itimer_accept() to ack a timer signal in signal
acceptance code, this a

Let itimer store itimerspec instead of itimerval, so I don't have to
convert to or from timeval frequently.

Introduce function itimer_accept() to ack a timer signal in signal
acceptance code, this allows us to return more fresh overrun counter
than at signal generating time. while POSIX says:
"the value returned by timer_getoverrun() shall apply to the most
recent expiration signal delivery or acceptance for the timer,.."
I prefer returning it at acceptance time.

Introduce SIGEV_THREAD_ID notification mode, it is used by thread
libary to request kernel to deliver signal to a specified thread,
and in turn, the thread library may use the mechanism to implement
SIGEV_THREAD which is required by POSIX.

Timer signal is managed by timer code, so it can not fail even if
signal queue is full filled by sigqueue syscall.

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Make p_itimers as a pointer, so file sys/proc.h does not need to include
sys/timers.h.

Make kernel structures invisible to userland.

Implement POSIX timers. Current only CLOCK_REALTIME and CLOCK_MONOTONIC
clock are supported. I have plan to merge XSI timer ITIMER_REAL and other
two CPU timers into the new code, current three slots

Implement POSIX timers. Current only CLOCK_REALTIME and CLOCK_MONOTONIC
clock are supported. I have plan to merge XSI timer ITIMER_REAL and other
two CPU timers into the new code, current three slots are available for
the XSI timers.
The SIGEV_THREAD notification type is not supported yet because our
sigevent struct lacks of two member fields:
sigev_notify_function
sigev_notify_attributes
I have found the sigevent is used in AIO, so I won't add the two members
unless the AIO code is adjusted.

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/* -> /*- for license, minor formatting changes

$Id$ -> $FreeBSD$

Back out part 1 of the MCFH that changed $Id$ to $FreeBSD$. We are not
ready for it yet.

Make the long-awaited change from $Id$ to $FreeBSD$

This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so

Make the long-awaited change from $Id$ to $FreeBSD$

This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.

Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.

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Obtained from: uthreads package