lockf: allow locking file descriptors

This is most useful inside a shell script, allowing one to lock just
portions of a script rather than having to wrap the entire script in a
lock.

PR: 262738
Reviewed by: 0mp, allanjude (both previous versions)
Co-authored-by: Daniel O'Connor <darius@dons.net.au>
Sponsored by: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D42718

Remove $FreeBSD$: two-line nroff pattern

Remove /^\.\\"\n\.\\"\s*\$FreeBSD\$$\n/

Remove whitespace which accidentaly snuck into r364831.

Add -w option to lockf(1).

By default, lockf(1) opens its lock file O_RDONLY|O_EXLOCK. On NFS, if the
file already exists, this is split into opening the file read-only and then
requesting an exclusive lock -- and the second step fails because NFS does
not permit exclusive locking on files which are opened read-only.

The new -w option changes the open flags to O_WRONLY|O_EXLOCK, allowing it
to work on NFS -- at the cost of not working if the file cannot be opened
for writing.

(Whether the traditional BSD behaviour of allowing exclusive locks to be
obtained on a file which cannot be opened for writing is a good idea is
perhaps questionable since it may allow less-privileged users to perform
a local denial of service; however this behaviour has been present for a
long time and changing it now seems like it would cause problems.)

Reviewed by: rmacklem
Differential Revision: https://reviews.freebsd.org/D26005

lockf(1): Add EXAMPLES section

* Add pretty small EXAMPLES section
* While here, fix a warning in line 98 (new sentence in new line)

Approved by: bcr@
Differential Revision: https://reviews.freebsd.org/D25205

lockf(1): add a reference to lockf(3).

Submitted by: Conrad Meyer
MFC after: 1 week

use .Mt to mark up email addresses consistently (part3)

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

Add option to lockf to avoid creating a file if it does not exist.

PR: bin/170775
Submitted by: Matthew Story <matthewstory@gmail.com>
Reviewed by: scottl
MFC after: 1 week

Remove trailing whitespace per mdoc lint warning

Disussed with: gavin
No objection from: doc
Approved by: joel
MFC after: 3 days

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

mdoc: order prologue macros consistently by Dd/Dt/Os

Although groff_mdoc(7) gives another impression, this is the ordering
most widely used and also required by mdocml/mandoc.

Reviewed by: ru
Approved by: philip, ed (mentors)

Create the altix project branch. The altix project will add support
for the SGI Altix 350 to FreeBSD/ia64. The hardware used for porting
is a two-module system, consisting of a base compute module and a
CPU expansion module. SGI's NUMAFlex architecture can be an excellent
platform to test CPU affinity and NUMA-aware features in FreeBSD.

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

Lockf was exiting with status 1 if the command did not exit normally.
This is easy to confuse with the actual exit status of the program.
Instead exit with EX_SOFTWARE if the command doesn't exit normally.

MFC after: 1 month

Also fix a "blank line" issue that sneaked in from rev. 1.19.

Submitted by: John Hein

Remove newly acquired hard sentence breaks.

Revision 1.12 of lockf.c fixed a "thundering herd" scenario when the
lock experienced contention a number of processes would race to acquire
lock when it was released. This problem resulted in a lot of CPU
load as well as locks being picked up out of order.

Unfortunately, a regression snuck in which allowed multiple threads
to pickup the same lock when -k was not used. This could occur when
multiple processes open a file descriptor to inode X (one process
will be blocked) and the file is unlinked on unlock (thereby removing
the directory entry allow another process to create a new directory
entry for the same file name and lock it).

This changes restores the old algorithm of: wait for the lock, then
acquire lock when we want to unlink the file on exit (specifically
when -k is not used) and keeps the new algorithm for when -k is used,
which yields fairness and improved performance.

Also, update the man page to inform users that if lockf(1) is being
used to facilitate concurrency between a number of processes, it
is recommended that -k be used to reduce CPU load and yeld
fairness with regard to lock ordering.

Collaborated with: jdp
PR: bin/114341
PR: bin/116543
PR: bin/111101
MFC after: 1 week

Markup cosmetics.

Fix all the spelling mistakes I could find in the man pages for words
that have at least 3 characters.

MFC after: 1 week
Thanks to: Music band ``Chingon''
for keeping me company while searching for these.

Markup and wording fixes.

Approved by: re (blanket)

Document a couple of gotchas.

Added the EXIT STATUS section where appropriate.

Mechanically kill hard sentence breaks.

Use `The .Nm utility'

mdoc(7) police: s/BSD/.Bx/ where appropriate.

Remove whitespace at EOL.

mdoc(7) police: removed HISTORY info from the .Os call.

Add history.

$Id$ -> $FreeBSD$

Add a "-k" option, to specify that the lock file should be kept
rather than removed.

Submitted by: Nick Barnes <Nick.Barnes@pobox.com>

.Sh AUTHOR -> .Sh AUTHORS. Use .An/.Aq.

Revert $FreeBSD$ to $Id$

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.

On failure, return various exit codes from <sysexits.h>. In particular,
return EX_TEMPFAIL if the file was already locked. This makes it easier
to distinguish between lock collisions and failures within the command
being executed.

Also, don't complain if the unlink() fails in the cleanup handler. It
doesn't matter anyway, and it obscured the exit status returned from
the command that was executed.

Initial import of the lockf utility. It executes an arbitrary command
while holding an exclusive lock on a file.