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To: Greg KH <greg@kroah.com>
Cc: Johannes Erdfelt <johannes@erdfelt.com>, linux-kernel@vger.kernel.org
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From: Roland Dreier <roland@topspin.com>
Date: Wed, 24 Nov 2004 11:23:37 -0800
In-Reply-To: <20041123183813.GA31068@kroah.com> (Greg KH's message of "Tue,
 23 Nov 2004 10:38:14 -0800")
Message-ID: <52u0rfyrt2.fsf@topspin.com>
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    Greg> No.  RCU is covered by a patent that only allows for it to
    Greg> be implemented in GPL licensed code.  If you want to use RCU
    Greg> in non-GPL code, you need to sign a license agreement with
    Greg> the holder of the RCU patent.

Not to stir up the flames any further (and this is really a moot point
since I got rid of our use of RCU)...

But given that I could implement the same API as in rcupdate.h as
below without using IBM's patented technique, how does merely using
this API cause code to require a patent license?

Thanks,
 Roland

/*
 * Copyright (c) 2004 Topspin Communications.  All rights reserved.
 * 
 * Usage of the works is permitted provided that this instrument is
 * retained with the works, so that any entity that uses the works is
 * notified of this instrument.
 *
 * DISCLAIMER: THE WORKS ARE WITHOUT WARRANTY.
 */

#ifndef MYRCU_H
#define MYRCU_H

struct rcu_head { };

#define rcu_read_lock		lock_kernel()
#define rcu_read_unlock		unlock_kernel()

#define rcu_dereference(p)	(p)
#define rcu_assign_pointer(p,v)	do { \
	lock_kernel(); \
	(p) = (v); \
	unlock_kernel(); \
} while (0)

static inline void call_rcu(struct rcu_head *head,
			    void (*func)(struct rcu_head *head))
{
	lock_kernel();
	func(head);
	unlock_kernel();
}

#endif /* MYRCU_H */
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