summaryrefslogtreecommitdiff
path: root/fs/xfs/xfs_behavior.h
blob: e7ca1fed955a98ff3e15a68ac1dddcdf9e1e020a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
/*
 * Copyright (c) 2000-2003,2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms 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.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#ifndef __XFS_BEHAVIOR_H__
#define __XFS_BEHAVIOR_H__

/*
 * Header file used to associate behaviors with virtualized objects.
 *
 * A virtualized object is an internal, virtualized representation of
 * OS entities such as persistent files, processes, or sockets.  Examples
 * of virtualized objects include vnodes, vprocs, and vsockets.  Often
 * a virtualized object is referred to simply as an "object."
 *
 * A behavior is essentially an implementation layer associated with
 * an object.  Multiple behaviors for an object are chained together,
 * the order of chaining determining the order of invocation.  Each
 * behavior of a given object implements the same set of interfaces
 * (e.g., the VOP interfaces).
 *
 * Behaviors may be dynamically inserted into an object's behavior chain,
 * such that the addition is transparent to consumers that already have
 * references to the object.  Typically, a given behavior will be inserted
 * at a particular location in the behavior chain.  Insertion of new
 * behaviors is synchronized with operations-in-progress (oip's) so that
 * the oip's always see a consistent view of the chain.
 *
 * The term "interposition" is used to refer to the act of inserting
 * a behavior such that it interposes on (i.e., is inserted in front
 * of) a particular other behavior.  A key example of this is when a
 * system implementing distributed single system image wishes to
 * interpose a distribution layer (providing distributed coherency)
 * in front of an object that is otherwise only accessed locally.
 *
 * Note that the traditional vnode/inode combination is simply a virtualized
 * object that has exactly one associated behavior.
 *
 * Behavior synchronization is logic which is necessary under certain
 * circumstances that there is no conflict between ongoing operations
 * traversing the behavior chain and those dynamically modifying the
 * behavior chain.  Because behavior synchronization adds extra overhead
 * to virtual operation invocation, we want to restrict, as much as
 * we can, the requirement for this extra code, to those situations
 * in which it is truly necessary.
 *
 * Behavior synchronization is needed whenever there's at least one class
 * of object in the system for which:
 * 1) multiple behaviors for a given object are supported,
 * -- AND --
 * 2a) insertion of a new behavior can happen dynamically at any time during
 *     the life of an active object,
 *	-- AND --
 *	3a) insertion of a new behavior needs to synchronize with existing
 *	    ops-in-progress.
 *	-- OR --
 *	3b) multiple different behaviors can be dynamically inserted at
 *	    any time during the life of an active object
 *	-- OR --
 *	3c) removal of a behavior can occur at any time during the life of
 *	    an active object.
 * -- OR --
 * 2b) removal of a behavior can occur at any time during the life of an
 *     active object
 *
 */

/*
 * Behavior head.  Head of the chain of behaviors.
 * Contained within each virtualized object data structure.
 */
typedef struct bhv_head {
	struct bhv_desc *bh_first;	/* first behavior in chain */
} bhv_head_t;

/*
 * Behavior descriptor.	 Descriptor associated with each behavior.
 * Contained within the behavior's private data structure.
 */
typedef struct bhv_desc {
	void		*bd_pdata;	/* private data for this behavior */
	void		*bd_vobj;	/* virtual object associated with */
	void		*bd_ops;	/* ops for this behavior */
	struct bhv_desc *bd_next;	/* next behavior in chain */
} bhv_desc_t;

/*
 * Behavior identity field.  A behavior's identity determines the position
 * where it lives within a behavior chain, and it's always the first field
 * of the behavior's ops vector. The optional id field further identifies the
 * subsystem responsible for the behavior.
 */
typedef struct bhv_identity {
	__u16	bi_id;		/* owning subsystem id */
	__u16	bi_position;	/* position in chain */
} bhv_identity_t;

typedef bhv_identity_t bhv_position_t;

#define BHV_IDENTITY_INIT(id,pos)	{id, pos}
#define BHV_IDENTITY_INIT_POSITION(pos) BHV_IDENTITY_INIT(0, pos)

/*
 * Define boundaries of position values.
 */
#define BHV_POSITION_INVALID	0	/* invalid position number */
#define BHV_POSITION_BASE	1	/* base (last) implementation layer */
#define BHV_POSITION_TOP	63	/* top (first) implementation layer */

/*
 * Plumbing macros.
 */
#define BHV_HEAD_FIRST(bhp)	(ASSERT((bhp)->bh_first), (bhp)->bh_first)
#define BHV_NEXT(bdp)		(ASSERT((bdp)->bd_next), (bdp)->bd_next)
#define BHV_NEXTNULL(bdp)	((bdp)->bd_next)
#define BHV_VOBJ(bdp)		(ASSERT((bdp)->bd_vobj), (bdp)->bd_vobj)
#define BHV_VOBJNULL(bdp)	((bdp)->bd_vobj)
#define BHV_PDATA(bdp)		(bdp)->bd_pdata
#define BHV_OPS(bdp)		(bdp)->bd_ops
#define BHV_IDENTITY(bdp)	((bhv_identity_t *)(bdp)->bd_ops)
#define BHV_POSITION(bdp)	(BHV_IDENTITY(bdp)->bi_position)

extern void bhv_head_init(bhv_head_t *, char *);
extern void bhv_head_destroy(bhv_head_t *);
extern int  bhv_insert(bhv_head_t *, bhv_desc_t *);
extern void bhv_insert_initial(bhv_head_t *, bhv_desc_t *);

/*
 * Initialize a new behavior descriptor.
 * Arguments:
 *   bdp - pointer to behavior descriptor
 *   pdata - pointer to behavior's private data
 *   vobj - pointer to associated virtual object
 *   ops - pointer to ops for this behavior
 */
#define bhv_desc_init(bdp, pdata, vobj, ops)		\
 {							\
	(bdp)->bd_pdata = pdata;			\
	(bdp)->bd_vobj = vobj;				\
	(bdp)->bd_ops = ops;				\
	(bdp)->bd_next = NULL;				\
 }

/*
 * Remove a behavior descriptor from a behavior chain.
 */
#define bhv_remove(bhp, bdp)				\
 {							\
	if ((bhp)->bh_first == (bdp)) {			\
		/*					\
		* Remove from front of chain.		\
		* Atomic wrt oip's.			\
		*/					\
	       (bhp)->bh_first = (bdp)->bd_next;	\
	} else {					\
	       /* remove from non-front of chain */	\
	       bhv_remove_not_first(bhp, bdp);		\
	}						\
	(bdp)->bd_vobj = NULL;				\
 }

/*
 * Behavior module prototypes.
 */
extern void		bhv_remove_not_first(bhv_head_t *bhp, bhv_desc_t *bdp);
extern bhv_desc_t *	bhv_lookup_range(bhv_head_t *bhp, int low, int high);
extern bhv_desc_t *	bhv_base(bhv_head_t *bhp);

/* No bhv locking on Linux */
#define bhv_base_unlocked	bhv_base

#endif /* __XFS_BEHAVIOR_H__ */