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/*
* Copyright (c) 2008, 2010, Oracle and/or its affiliates. All rights reserved.
* Use is subject to license terms.
*
* Copyright (c) 2012, Intel Corporation.
*
* Author: Nikita Danilov <nikita.danilov@sun.com>
*
* This file is part of Lustre, http://www.lustre.org.
*
* Lustre 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.
*
* Lustre is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Lustre; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
*/
#ifndef __LUSTRE_LU_REF_H
#define __LUSTRE_LU_REF_H
#include <linux/list.h>
/** \defgroup lu_ref lu_ref
*
* An interface to track references between objects. Mostly for debugging.
*
* Suppose there is a reference counted data-structure struct foo. To track
* who acquired references to instance of struct foo, add lu_ref field to it:
*
* \code
* struct foo {
* atomic_t foo_refcount;
* struct lu_ref foo_reference;
* ...
* };
* \endcode
*
* foo::foo_reference has to be initialized by calling
* lu_ref_init(). Typically there will be functions or macros to increment and
* decrement foo::foo_refcount, let's say they are foo_get(struct foo *foo)
* and foo_put(struct foo *foo), respectively.
*
* Whenever foo_get() is called to acquire a reference on a foo, lu_ref_add()
* has to be called to insert into foo::foo_reference a record, describing
* acquired reference. Dually, lu_ref_del() removes matching record. Typical
* usages are:
*
* \code
* struct bar *bar;
*
* // bar owns a reference to foo.
* bar->bar_foo = foo_get(foo);
* lu_ref_add(&foo->foo_reference, "bar", bar);
*
* ...
*
* // reference from bar to foo is released.
* lu_ref_del(&foo->foo_reference, "bar", bar);
* foo_put(bar->bar_foo);
*
*
* // current thread acquired a temporary reference to foo.
* foo_get(foo);
* lu_ref_add(&foo->reference, __func__, current);
*
* ...
*
* // temporary reference is released.
* lu_ref_del(&foo->reference, __func__, current);
* foo_put(foo);
* \endcode
*
* \e Et \e cetera. Often it makes sense to include lu_ref_add() and
* lu_ref_del() calls into foo_get() and foo_put(). When an instance of struct
* foo is destroyed, lu_ref_fini() has to be called that checks that no
* pending references remain. lu_ref_print() can be used to dump a list of
* pending references, while hunting down a leak.
*
* For objects to which a large number of references can be acquired,
* lu_ref_del() can become cpu consuming, as it has to scan the list of
* references. To work around this, remember result of lu_ref_add() (usually
* in the same place where pointer to struct foo is stored), and use
* lu_ref_del_at():
*
* \code
* // There is a large number of bar's for a single foo.
* bar->bar_foo = foo_get(foo);
* bar->bar_foo_ref = lu_ref_add(&foo->foo_reference, "bar", bar);
*
* ...
*
* // reference from bar to foo is released.
* lu_ref_del_at(&foo->foo_reference, bar->bar_foo_ref, "bar", bar);
* foo_put(bar->bar_foo);
* \endcode
*
* lu_ref interface degrades gracefully in case of memory shortages.
*
* @{
*/
/*
* dummy data structures/functions to pass compile for now.
* We need to reimplement them with kref.
*/
struct lu_ref {};
struct lu_ref_link {};
static inline void lu_ref_init(struct lu_ref *ref)
{
}
static inline void lu_ref_fini(struct lu_ref *ref)
{
}
static inline struct lu_ref_link *lu_ref_add(struct lu_ref *ref,
const char *scope,
const void *source)
{
return NULL;
}
static inline struct lu_ref_link *lu_ref_add_atomic(struct lu_ref *ref,
const char *scope,
const void *source)
{
return NULL;
}
static inline void lu_ref_add_at(struct lu_ref *ref,
struct lu_ref_link *link,
const char *scope,
const void *source)
{
}
static inline void lu_ref_del(struct lu_ref *ref, const char *scope,
const void *source)
{
}
static inline void lu_ref_set_at(struct lu_ref *ref, struct lu_ref_link *link,
const char *scope, const void *source0,
const void *source1)
{
}
static inline void lu_ref_del_at(struct lu_ref *ref, struct lu_ref_link *link,
const char *scope, const void *source)
{
}
static inline int lu_ref_global_init(void)
{
return 0;
}
static inline void lu_ref_global_fini(void)
{
}
static inline void lu_ref_print(const struct lu_ref *ref)
{
}
static inline void lu_ref_print_all(void)
{
}
/** @} lu */
#endif /* __LUSTRE_LU_REF_H */
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