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

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

poll(2): Add POLLRDHUP.

Teach poll(2) to support Linux-style POLLRDHUP events for sockets, if
requested. Triggered when the remote peer shuts down writing or closes
its end.

Reviewed by: kib
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D29757

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.

Add the ppoll() system call.
Export kern_poll() needed by an upcoming Linuxulator change.

Differential Revision: https://reviews.freebsd.org/D1133
Reviewed by: kib, wblock
MFC after: 1 month

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

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

Reconnect a comment with its code.

Submitted by: bde

Bring poll.h up to conformance with POSIX.1-2001 by adding some
visibility conditionals, adding the nfds_t type, and changing the
poll() prototype a little. Update the manual to match.

Cleanup comments.

Remove all current poll(2) extensions except POLLINIGNEOF as they are now
unused.

Submitted by: bde

Remove __P

Fix select on fifos.

Backout revision 1.56 and 1.57 of fifo_vnops.c.

Introduce a new poll op "POLLINIGNEOF" that can be used to ignore
EOF on a fifo, POLLIN/POLLRDNORM is converted to POLLINIGNEOF within
the FIFO implementation to effect the correct behavior.

This should allow one to view a fifo pretty much as a data source
rather than worry about connections coming and going.

Reviewed by: bde

Fix typo: compatability -> compatibility.

Compatability is not an existing english word.

Synchronize the poll() prototype with the one provided in the
poll(2) manual page.

PR: 20677
Submitted by: "Ralf S. Engelschall" <rse@engelschall.com>

Change #ifdef KERNEL to #ifdef _KERNEL in the public headers. "KERNEL"
is an application space macro and the applications are supposed to be free
to use it as they please (but cannot). This is consistant with the other
BSD's who made this change quite some time ago. More commits to come.

$Id$ -> $FreeBSD$

Cleaned up some comments and ifdefs.

Add support for poll(2) on files. vop_nopoll() now returns POLLNVAL
if one of the new poll types is requested; hopefully this will not break
any existing code. (This is done so that programs have a dependable
way of determining whether a filesystem supports the extended poll types
or not.)

The new poll types added are:

POLLWRITE - file contents may have been modified
POLLNLINK - file was linked, unlinked, or renamed
POLLATTRIB - file's attributes may have been changed
POLLEXTEND - file was extended

Note that the internal operation of poll() means that it is impossible
for two processes to reliably poll for the same event (this could
be fixed but may not be worth it), so it is not possible to rewrite
`tail -f' to use poll at this time.

oops, I accidently committed a version without INFTIM at the last moment.
I'm not sure that this is the right place to put it, it is 'supposed' to
live in stropts.h.

Add sys/poll.h