PostgreSQL licensed code on Linux

[Luis R. Rodriguez]

The question over future possible PostgreSQL licensed code on Linux came up
to me recently. While doing some quick of digging around I found code
already under such license it seems:

The file drivers/md/bcache/util.c has:

cafe563591446 (Kent Overstreet 2013-03-23 16:11:31 -0700 318) /*
cafe563591446 (Kent Overstreet 2013-03-23 16:11:31 -0700 319)  * Portions
Copyright (c) 1996-2001, PostgreSQL Global Development Group (Any
cafe563591446 (Kent Overstreet 2013-03-23 16:11:31 -0700 320)  * use
permitted, subject to terms of PostgreSQL license; see.)

That seems to indicate that we've had already PostgreSQL licensed code on
Linux since Kent's addition of bcache to Linux in 2013. The portion of code
is rather small though, to me it seems to cover only crc_table[],
bch_crc64_update(), and bch_crc64(). Four things:

a) This is the only code on Linux which seems to use PostgreSQL
b) The language for license seem to be cut off, 'see.' seems incomplete,
whereas typically it would point to a file with the full language text.
c) We can only infer what portions of the file are under this license
d) Even though some licenses claim to be GPL-Compatible, if possible we
should dual license such with the GPL if possible (*)

If some folks are considering adding yet more code to Linux which is
currently under a PostgreSQL license I figured reviewing the existing
PostgreSQL code's use may be a good start to set precedent for future work.
Since we already have at least one file with a PostgreSQL-sort-of boiler
plate it at least sets the precedent we have already sort of dealt with
PostgreSQL.

My recommendations:

As silly as it may be we should split out the PostgreSQL licensed code from
drivers/md/bcache/util.c into its own file and while at it clarify the
license.

If possible, if we can dual license this code with GPL it would be good as
it would do two things:

1) Removes any ambiguity in case of questions over GPL Compatibility in the
future about the PostgreSQL license

2) Other folks considering using PostgreSQL licensed code on Linux have a
template they can use

Other thoughts?

* Although some websites / organizations may state a license is GPL
compatible we have to be careful in the kernel as some companies or
organizations may disagree with some of these views (example is FSF's
website and position -- an example was one of the old BSD licenses which
some folks questioned its GPL compatibility with); despite the ambiguity
possible with dual licensing language [0], if  one chooses a clear language
it can be extremely useful and cautious on the kernel community's part.

[0]
https://www.softwarefreedom.org/resources/2007/gpl-non-gpl-collaboration.html

   Luis