This is intended as infrastructure to allow sepgsql to cooperate with
connection pooling software, by allowing the effective security label
to be set for each new connection.

KaiGai Kohei, reviewed by Yeb Havinga.

KaiGai Kohei

This is some preliminary refactoring related to a pending patch
to allow sepgsql-enable sessions to make dynamic label transitions.
But this commit doesn't involve any functional change: it just puts
some bits of code in more logical places.

KaiGai Kohei

KaiGai Kohei, reviewed by Dimitri Fontaine and me.

Because these tests require root privileges, not to mention invasive
changes to the security configuration of the host system, it's not
reasonable for them to be invoked by a regular "make check" or "make
installcheck".  Instead, dike out the Makefile's knowledge of the tests,
and change chkselinuxenv (now renamed "test_sepgsql") into a script that
verifies the environment is workable and then runs the tests.  It's
expected that test_sepgsql will only be run manually.

While at it, do some cleanup in the error checking in the script, and
do some wordsmithing in the documentation.

Robert Haas and KaiGai Kohei

This is still a bit of a hack, but it's better than the old way, for sure.

KaiGai Kohei, with one change by me to make it compile

KaiGai Kohei

Don't test whether the number of labels is numerically equal to zero;
count(*) isn't going return zero anyway, and the current coding blows
up if it returns an empty string or an error.

The previous coding resulted in contrib modules unintentionally overriding
the use of CONTRIB_TESTDB.  There seems no particularly good reason to
allow that (after all, the makefile can set CONTRIB_TESTDB if that's really
what it intends).

In passing, document REGRESS_OPTS where the other pgxs.mk options are
documented.

Back-patch to 9.1 --- in prior versions, there were no cases of contrib
modules setting REGRESS_OPTS without including the --dbname switch, so
while the coding was fragile there was no actual bug.

Eliminate dependencies on "which", as we don't really need that to be
installed for proper testing.  Don't number the tests, as that increases
the footprint of every patch that wants to add or remove tests.  Make
the test output more informative, so that it's a bit easier to see what
went right (or wrong).  Spelling and grammar improvements.

contrib/xml2 can get by without libxslt; the relevant features just
won't work.  But if doesn't have libxml2, or if sepgsql doesn't have
libselinux, the link succeeds but the module then fails to work at load
time.  To avoid that, link the require libraries unconditionally, so
that it will be clear at link-time that there is a problem.

Per discussion with Tom Lane and KaiGai Kohei.

KaiGai Kohei, with some changes by me.

This probably needs more work, but it's a start.

KaiGai Kohei

The previous functions of assign hooks are now split between check hooks
and assign hooks, where the former can fail but the latter shouldn't.
Aside from being conceptually clearer, this approach exposes the
"canonicalized" form of the variable value to guc.c without having to do
an actual assignment.  And that lets us fix the problem recently noted by
Bernd Helmle that the auto-tune patch for wal_buffers resulted in bogus
log messages about "parameter "wal_buffers" cannot be changed without
restarting the server".  There may be some speed advantage too, because
this design lets hook functions avoid re-parsing variable values when
restoring a previous state after a rollback (they can store a pre-parsed
representation of the value instead).  This patch also resolves a
longstanding annoyance about custom error messages from variable assign
hooks: they should modify, not appear separately from, guc.c's own message
about "invalid parameter value".

KaiGai Kohei

Instead, document how to build it manually.

Per discussion.  KaiGai Kohei, with some wordsmithing by me.

KaiGai Kohei

Robert Haas, with a few suggestions from Thom Brown

This is still pretty rough - among other things, the documentation
needs work, and the messages need a visit from the style police -
but this gets the basic framework in place.

KaiGai Kohei