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Implement mrlocks on top of rwsems, instead of using our own mrlock code.

/*
 * Copyright (c) 2000-2004 Silicon Graphics, Inc.  All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Further, this software is distributed without any warranty that it is
 * free of the rightful claim of any third person regarding infringement
 * or the like.  Any license provided herein, whether implied or
 * otherwise, applies only to this software file.  Patent licenses, if
 * any, provided herein do not apply to combinations of this program with
 * other software, or any other product whatsoever.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write the Free Software Foundation, Inc., 59
 * Temple Place - Suite 330, Boston MA 02111-1307, USA.
 *
 * Contact information: Silicon Graphics, Inc., 1600 Amphitheatre Pkwy,
 * Mountain View, CA  94043, or:
 *
 * http://www.sgi.com
 *
 * For further information regarding this notice, see:
 *
 * http://oss.sgi.com/projects/GenInfo/SGIGPLNoticeExplan/
 */
#ifndef __XFS_SUPPORT_MRLOCK_H__
#define __XFS_SUPPORT_MRLOCK_H__

#include <linux/rwsem.h>

enum { MR_NONE, MR_ACCESS, MR_UPDATE };

typedef struct {
	struct rw_semaphore	mr_lock;
	int			mr_writer;
} xfs_mrlock_t;

#define mrinit(mrp, name)	\
	( (mrp)->mr_writer = 0, init_rwsem(&(mrp)->mr_lock) )
#define mrlock_init(mrp, t,n,s)	mrinit(mrp, n)
#define mrfree(mrp)		do { } while (0)
#define mraccess(mrp)		mraccessf(mrp, 0)
#define mrupdate(mrp)		mrupdatef(mrp, 0)

static inline void mraccessf(xfs_mrlock_t *mrp, int flags)
{
	down_read(&mrp->mr_lock);
}

static inline void mrupdatef(xfs_mrlock_t *mrp, int flags)
{
	down_write(&mrp->mr_lock);
	mrp->mr_writer = 1;
}

static inline int mrtryaccess(xfs_mrlock_t *mrp)
{
	return down_read_trylock(&mrp->mr_lock);
}

static inline int mrtryupdate(xfs_mrlock_t *mrp)
{
	if (!down_write_trylock(&mrp->mr_lock))
		return 0;
	mrp->mr_writer = 1;
	return 1;
}

static inline void mrunlock(xfs_mrlock_t *mrp)
{
	if (mrp->mr_writer) {
		mrp->mr_writer = 0;
		up_write(&mrp->mr_lock);
	} else {
		up_read(&mrp->mr_lock);
	}
}

static inline void mrdemote(xfs_mrlock_t *mrp)
{
	mrp->mr_writer = 0;
	downgrade_write(&mrp->mr_lock);
}

/*
 * Debug-only routine, without some platform-specific asm code, we can
 * now only answer requests regarding whether we hold the lock for write
 * (reader state is outside our visibility, we only track writer state).
 * Note: means !ismrlocked would give false positivies, so don't do that.
 */
static inline int ismrlocked(xfs_mrlock_t *mrp, int type)
{
	if (type == MR_UPDATE)
		return mrp->mr_writer;
	return 1;
}

#endif /* __XFS_SUPPORT_MRLOCK_H__ */