MFC r297160,r297196:

r297160:
Document openat(2) behavior.
r297196:
Spell out 'system calls'.

MFC r271049:

Note that script(1) consumes filemon(4).

MFC r297156,r297157,r297158,r297159,r297161,r297172,r297200,r297201,r297202,
r297203,r297256:

r297156:
Track filemon usage via a proc.p_filemon pointer rather than its own lists.
r297157:
Stop tracking stat(2).
r297158:
Consolidate open(2) and openat(2) code.
r297159:
Use curthread for vn_fullpath.
r297161:
Attempt to use the namecache for openat(2) path resolution.
r297172:
Consolidate common link(2) logic.
r297200:
Follow-up r297156: Close the log in filemon_dtr rather than in the last
reference.
r297201:
Return any log write failure encountered when closing the filemon fd.
r297202:
Remove unused done argument to copyinstr(9).
r297203:
Handle copyin failures.
r297256:
Remove unneeded return left from refactoring.

Relnotes: yes (filemon stability/performance updates)
Sponsored by: EMC / Isilon Storage Division

MFC r296286,r296470,r296472,r296473,r296575:

r296286:
Remove filemon->lock wrappers.
r296470:
Only call bwillwrite() for logging to vnodes, as other fo_write() calls do.
r296472:
Require kldunload -f to unload.
r296473:
Add missing break for r296472.
r296575:
FILEMON_SET_FD: Disallow changing the fd.

MFC r294933,r294949,r294952,r294953,r294957,r294965,r294967,r294968,r295017,
r295026,r295027,r295029,r295030,r295649:

r294933:
Drop any previous fd when setting a new one.
r294949:
filemon_ioctl: Handle error from devfs_get_cdevpriv(9).
r294952:
filemon_ioctl: Lock the associated filemon handle before writing to it.
r294953:
filemon_comment has nothing to do with wrappers so move it out of
filemon_wrapper.c.
r294957:
filemon_dtr: Lock the associated filemon handle before writing to it.
r294965:
filemon: Use process_exit EVENTHANDLER to capture process exit.
r294967:
filemon: Trace fork via process_fork event.
r294968:
Follow-up r294967: Mark flags unused.
r295017:
filemon: Use process_exec EVENTHANDLER to capture sys_execve.
r295026:
filemon_open: Don't record a process to trace here.
r295027:
filemon: Track the process pointer rather than a pid.
r295029:
Document the purpose and non-purpose of filemon(4).
r295030:
Note the double fork behavior with filemon.
r295649:
filemon: Fix panic when fork1() is called from kproc_create().

Approved by: re (marius)

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

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

Fix and improve filemon(4) example:
- remove return statements from void function [1]
- include missing header
- use O_CLOEXEC instead of separate fcntl() calls

PR: docs/179459 [1]
MFC after: 1 week

Add to the description and spell check.

mdoc police.

Submitted by: ru
Much thanks to: ru

Various mdoc fixes.

Correct examples to the latest version I had.

Add a man page for filemon(4) [r236592].