Re: Non-GPL export of invalidate_mmap_range

[Andrew Morton]

Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> I don't understand why IBM is pushing this dubious change right now,

It isn't a dubious change, on technical grounds.  It is reasonable for a
distributed filesystem to want to be able to shoot down pte's which map
sections of pagecache.  Just as it is reasonable for the filesystem to be
able to shoot down the pagecache itself.

We've exported much lower-level stuff than this, because some in-kernel
module happened to use it.


> GPL violation and thus copyright violation issues in Linux is the
> last thing IBM wants to see in the press with the current mess going
> on, right?

Well this is a chicken-and-egg, isn't it.  The only way in which we can
audit the IBM code for its derivedness is for the source to be made
available.  Although not necessarily under GPL.  Or we accept Paul's claim,
which I personally am inclined to do.


Look, this isn't going anywhere.  We have a perfectly reasonable request
from Paul to make this symbol available for IBM's filesystem.  The usual
way to handle this sort of thing is to say "ooh.  shit.  hard." and not
reply to the email.  That is not adequate and hopefully Paul will not let
us get away with it.

We need to give Paul a reasoned and logically consistent answer to his
request.  For that we need to establish some sort of framework against
which to make a decision and then make the decision.  

One approach is a fait-accomplis from the top-level maintainer.  Here,
we're trying to do it in a different way.

I have proposed two criteria upon which this should be judged:

a) Does the export make technical sense?  Do filesystems have
   legitimate need for access to this symbol?

(really, a) is sufficient grounds, but for real-world reasons:)

b) Does the IBM filsystem meet the kernel's licensing requirements?


It appears that the answers are a): yes and b) probably.

Please, feel free to add additional criteria.  We could also ask "do we
want to withhold this symbols to encourage IBM to GPL the filesystem" or
"do we simply refuse to export any symbol which is not used by any GPL
software" (if so, why?).  Over to you.


But at the end of the day, if we decide to not export this symbol, we owe
Paul a good, solid reason, yes?
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