MF11 304617: Fix various nits in the aio operation manpages.

- Avoid double use of "request" in a single sentence. Instead, describe
aio_sigevent as being used to request notification of the associated
operation's completion. This matches the language used to describe
aio_sigevent in aio(4).
- Simplify the prohibition on modifying buffers while requests are in
flight.
- Fix case mismatch.
- Drop note about not using stack variables. C programmers should be able
to figure out if a stack variable is safe based on the later warning
about the life cycle requirements of control blocks.
- Remove prohibition on modifying the I/O buffer for aio_fsync() since
it does not use an I/O buffer. For aio_mlock(), prohibit modifications
to the mapping (e.g. due to mprotect, munmap, mmap, etc.) but do not
prohibit modifications to the memory backing the buffer (stores into
the pages backing the buffer).

Approved by: re (kib)

MF11 304617: Fix various nits in the aio operation manpages.

- Avoid double use of "request" in a single sentence. Instead, describe
aio_sigevent as being used to request notification of the associated
operation's completion. This matches the language used to describe
aio_sigevent in aio(4).
- Simplify the prohibition on modifying buffers while requests are in
flight.
- Fix case mismatch.
- Drop note about not using stack variables. C programmers should be able
to figure out if a stack variable is safe based on the later warning
about the life cycle requirements of control blocks.
- Remove prohibition on modifying the I/O buffer for aio_fsync() since
it does not use an I/O buffer. For aio_mlock(), prohibit modifications
to the mapping (e.g. due to mprotect, munmap, mmap, etc.) but do not
prohibit modifications to the memory backing the buffer (stores into
the pages backing the buffer).

Approved by: re (kib)

Copy stable/11@r303970 to releng/11.0 as part of the 11.0-RELEASE
cycle.

Prune svn:mergeinfo from the new branch, and rename it to RC1.

Update __FreeBSD_version.

Use the quarterly branch for the default FreeBSD.conf pkg(8) repo and
the dvd1.iso packages population.

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

MFC 303164: Add more documentation regarding unsafe AIO requests.

The asynchronous I/O changes made previously result in different
behavior out of the box. Previously all AIO requests failed with
ENOSYS / SIGSYS unless aio.ko was explicitly loaded. Now, some AIO
requests complete and others ("unsafe" requests) fail with EOPNOTSUPP.

Reword the introductory paragraph in aio(4) to add a general
description of AIO before describing the vfs.aio.enable_unsafe sysctl.

Remove the ENOSYS error description from aio_fsync(2), aio_read(2),
and aio_write(2) and replace it with a description of EOPNOTSUPP.

Remove the ENOSYS error description from aio_mlock(2).

Log a message to the system log the first time a process requests an
"unsafe" AIO request that fails with EOPNOTSUPP. This is modeled on
the log message used for processes using the legacy pty devices.

Approved by: re (gjb)

MFC 302899: Add documentation for the sigevent structure.

- Add a sigevent(3) manpage to give a general overview of the sigevent
structure and the available notification mechanisms.
- Document that AIO requests contain a nested sigevent structure that can
be used to request completion notification.
- Expand the sigevent details in other manuals to note details such as
the extra values stored in a queued signal's information or in a posted
kevent.

Approved by: re (gjb)

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

use .Mt to mark up email addresses consistently (part4)

PR: 191174
Submitted by: Franco Fichtner <franco at lastsummer.de>

Fix an apparent typo.

MFC after: 3 days

Minor mdoc fixes.

Add new system call - aio_mlock(). The name speaks for itself. It allows
to perform the mlock(2) operation, which can consume a lot of time, under
control of aio(4).

Reviewed by: kib, jilles
Sponsored by: Nginx, Inc.