linux-kernel - Re: x86/fpu: Don't export __kernel_fpu

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Date:   Thu, 10 Jan 2019 19:24:13 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     "Hutter, Tony" <hutter2@...l.gov>,
        Marc Dionne <marc.c.dionne@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: x86/fpu: Don't export __kernel_fpu_{begin,end}()

On Thu, Jan 10, 2019 at 07:07:52PM +0100, Sebastian Andrzej Siewior wrote:
> On 2019-01-10 17:32:58 [+0000], Hutter, Tony wrote:
> > > But since when did out-of-tree modules use __kernel_fpu_begin?  It's an
> > > x86-only thing, and shouldn't really be used by anyone, right?
> > 
> > ZFS on Linux uses it for checksums.  Its removal is currently breaking ZFS builds against 5.0:
> 
> So btrfs uses crc32c() / kernel's crypto API for that and ZFS can't?
> Well the crypto API is GPL only exported so that won't work. crc32c() is
> EXPORT_SYMBOL() so it would work.
> On the other hand it does not look right to provide a EXPORT_SYMBOL
> wrapper around a GPL only interface…

Yes, the "GPL condom" attempt doesn't work at all.  It's been shot down
a long time ago in the courts.

My tolerance for ZFS is pretty non-existant.  Sun explicitly did not
want their code to work on Linux, so why would we do extra work to get
their code to work properly?

greg k-h