C. Thomas Tyler
Defend against environment hijacking of P4ENVIRO.

== Background ==

A core benefit of the SDP is the controlled, easily understood
environment, both shell environment and Perforce context settings.
These configuration items are carefully controlled in the SDP's config
files and environment loading mechanism in p4_vars.

The new-ish (2015.1) behavior of 'p4 set' to persist values on
Unix/Linux is detrimental in an SDP environment, which is designed
for live production servers.  That hijacking capability is perfect
for what it was intended for (mainly for DVCS usage, so a 'p4 clone'
can hijack an individual user's P4CONFIG setting).  But I am not sure
there's a need for that on the production server, and allowing it can
impact reliability/robustness of core SDP operations.

Folks can always set P4ENVIRO separately or unset it (defaulting
to ~/.p4enviro) if they want for some non-SDP reason on the
production server.  Ditto for P4CONFIG.

== Shell Environment Management ==

The p4d trigger and p4broker filter scripts inherit their shell
environment from the corresponding p4d or p4broker server process. Thus,
the benefit of the SDP controlled environment mechanism includes
supplemental automation, such as triggers and broker filter scripts.

While the shell environment can't change after the server processes
start, the Perforce context settings (P4PORT, P4CLIENT, P4USER, etc.)
can be changed at any time by adjusting the contents of the
P4CONFIG and/or P4ENVIRO files.

Historically, P4CONFIG (which has been around for a long while) hasn't
been an issue with the SDP, perhaps because changing the context
settings is well-understood, and/or perhaps because it requires
modifying a file on disk, which seems like a "big deal" when you're
working on a production server machine.

Lately, I've been finding that P4ENVIRO is a bit more prone to
abuse.  Maybe that's because folks don't understand it or its
impact well; they do a 'p4 set' command to persist values for
context settings (e.g. P4CONFIG) while logged in as 'perforce'
on the production server, thinking they're just affecting their own
shell environment, and inadvetently busting triggers or broker

An admin might do a 'p4 set' command for personal reasons in an
SDP-managed environment, and unexpectedly sabotage checkpoint
scripts (e.g. p4 set P4PORT=9999), since values persisted with
'p4 set' outrank those defined in the SDP's carefully controlled
shell environment.  P4ENVIRO outranks even P4CONFIG, and P4ENVIRO
also has capability to hijack the P4CONFIG value itself.

== The Goal ==

The goal with this proposed change is to expliclty disable the two
mechanisms, P4CONFIG and P4ENVIRO, which can impact the Perforce
context settings after the server process has started.

The change: Simply point both P4CONFIG and P4ENVIRO to invalid paths
under /dev/null.

Now, one could argue that 'p4 set' is functioning as designed, and
that disabling this default behavior (a feature of the product), is
more unexpected than leaving it alone.  I submit that in an SDP
environment designed to live on production servers, this is OK, as the
higher objective is stability for production environments.

== Side Effects for P4CONFIG ==

AFAIK, the P4CONFIG file defined in the SDP is not used.  It just
defines a value that points to an empty file (e.g. /p4/1/.p4config),
then we don't put anything into it.  This change would make it impossible to put
anything into it.

== Side Effects for P4ENVIRO ==

This change would effectively disable the ability to use the 'p4 set'
command to persist values in a Unix/Linux environment.  The 'p4 set'
command can still be used to query values.  Attempts to persist values,
e.g. 'p4 set P4PORT=9999', are greeted with this error:

Perforce client error:
Can't set registry on UNIX.
open for write: /dev/null/.p4enviro: Not a directory

== Scope ==

This job is for the Unix/Linx SDP only.  The concepts applies as
ready for Windows, but the mechanics are dramatically different,
and considerations are different due to the reliance on the Windows
registry on Windows.  That entire discussion deserves a separate job.
Reported By
Reported Date
Modified By
Modified Date
Owned By
Dev Notes
This job, SDP-67, was originally named job000548.

[2016/07/07 ttyler]: The original title of this review was:
Defend against environment hijacking of P4ENVIRO and P4CONFIG.

Per review, it was decided to change behavior only for P4ENVRIO, and
to leave the original SDP setting for P4CONFIG in place.  The job
title was changed to reflect this.