Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

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

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

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

Finish off style(9) fixes which I started two revisions ago. This basically
changes the indentation style from 4 spaces to 8 spaces which we expect to
see in other FreeBSD source files.

Woops, in my previous commit, I actually committed some style changes with
a functional change. I know this is a big no no, so this is a forced commit
to note the functional changes from my previous revision:

@@ -196,7 +176,7 @@ wait_for_lock(const char *name, int flag
int fd;

if ((fd = open(name, O_CREAT|O_RDONLY|O_EXLOCK|flags, 0666)) == -1) {
- if (errno == ENOENT || errno == EINTR || errno == EAGAIN)
+ if (errno == EINTR || errno == EAGAIN)
return (-1);
err(EX_CANTCREAT, "cannot open %s", name);
}

Do not ignore ENOENT

Pointed out by: Amir Shalem

Un-break handling of -t 0 which was broken in my previous commit.
Add a flags argument to wait_for_lock so that O_NONBLOCK can be
passed to open if a user doesn't want the open to sleep until the
lock becomes available.

Submitted by: Amir Shalem (partially modified)

Fix long standing race condition associated with how lockf uses open(2)
for mutual exclusion:

A brief description of the problem:

1) Proc A picks up non-blocking lock on file X
2) Proc B attempts to pickup lock, fails then waits
3) Proc C attempts to pickup lock, fails then waits
4) Proc A releases lock
5) Proc B acquires lock, release it to pickup a non-blocking version
6) Proc C acquires lock, release it to pickup a non-blocking version
7) Both process B and C race each other to pickup lock again

This occurs mainly because the processes do not keep the lock after they have
been waiting on it. They drop it, attempt to re-acquire it. (They use the wait
to notify when the lock has become available then race to pick it up). This
results in additional CPU utilization during the race, and can also result
in processes picking locks up out of order.

This change attempts to correct this problem by eliminating the test/acquire
race and having the operating system handle it.

Reported by: kris
Tested by: kris
MFC after: 1 week

Use warn() instead of perror().

Consistently use FBSDID

Warns cleanups.

$Id$ -> $FreeBSD$

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

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

lockf: usage : lockf -> usage: lockf by using fprintf instead of errx.

compare return value from getopt against -1 rather than EOF, per the final
posix standard on the topic.

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.

This commit was generated by cvs2svn to compensate for changes in r21439,
which included commits to RCS files with non-trunk default branches.

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