fs/xfs/xfs_behavior.h

   1 /*
   2  * Copyright (c) 2000-2003,2005 Silicon Graphics, Inc.
   3  * All Rights Reserved.
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License as
   7  * published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope that it would be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write the Free Software Foundation,
  16  * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  17  */
  18 #ifndef __XFS_BEHAVIOR_H__
  19 #define __XFS_BEHAVIOR_H__
  20
  21 /*
  22  * Header file used to associate behaviors with virtualized objects.
  23  *
  24  * A virtualized object is an internal, virtualized representation of
  25  * OS entities such as persistent files, processes, or sockets.  Examples
  26  * of virtualized objects include vnodes, vprocs, and vsockets.  Often
  27  * a virtualized object is referred to simply as an "object."
  28  *
  29  * A behavior is essentially an implementation layer associated with
  30  * an object.  Multiple behaviors for an object are chained together,
  31  * the order of chaining determining the order of invocation.  Each
  32  * behavior of a given object implements the same set of interfaces
  33  * (e.g., the VOP interfaces).
  34  *
  35  * Behaviors may be dynamically inserted into an object's behavior chain,
  36  * such that the addition is transparent to consumers that already have
  37  * references to the object.  Typically, a given behavior will be inserted
  38  * at a particular location in the behavior chain.  Insertion of new
  39  * behaviors is synchronized with operations-in-progress (oip's) so that
  40  * the oip's always see a consistent view of the chain.
  41  *
  42  * The term "interposition" is used to refer to the act of inserting
  43  * a behavior such that it interposes on (i.e., is inserted in front
  44  * of) a particular other behavior.  A key example of this is when a
  45  * system implementing distributed single system image wishes to
  46  * interpose a distribution layer (providing distributed coherency)
  47  * in front of an object that is otherwise only accessed locally.
  48  *
  49  * Note that the traditional vnode/inode combination is simply a virtualized
  50  * object that has exactly one associated behavior.
  51  *
  52  * Behavior synchronization is logic which is necessary under certain
  53  * circumstances that there is no conflict between ongoing operations
  54  * traversing the behavior chain and those dynamically modifying the
  55  * behavior chain.  Because behavior synchronization adds extra overhead
  56  * to virtual operation invocation, we want to restrict, as much as
  57  * we can, the requirement for this extra code, to those situations
  58  * in which it is truly necessary.
  59  *
  60  * Behavior synchronization is needed whenever there's at least one class
  61  * of object in the system for which:
  62  * 1) multiple behaviors for a given object are supported,
  63  * -- AND --
  64  * 2a) insertion of a new behavior can happen dynamically at any time during
  65  *     the life of an active object,
  66  *      -- AND --
  67  *      3a) insertion of a new behavior needs to synchronize with existing
  68  *          ops-in-progress.
  69  *      -- OR --
  70  *      3b) multiple different behaviors can be dynamically inserted at
  71  *          any time during the life of an active object
  72  *      -- OR --
  73  *      3c) removal of a behavior can occur at any time during the life of
  74  *          an active object.
  75  * -- OR --
  76  * 2b) removal of a behavior can occur at any time during the life of an
  77  *     active object
  78  *
  79  */
  80
  81 /*
  82  * Behavior head.  Head of the chain of behaviors.
  83  * Contained within each virtualized object data structure.
  84  */
  85 typedef struct bhv_head {
  86         struct bhv_desc *bh_first;      /* first behavior in chain */
  87 } bhv_head_t;
  88
  89 /*
  90  * Behavior descriptor.  Descriptor associated with each behavior.
  91  * Contained within the behavior's private data structure.
  92  */
  93 typedef struct bhv_desc {
  94         void            *bd_pdata;      /* private data for this behavior */
  95         void            *bd_vobj;       /* virtual object associated with */
  96         void            *bd_ops;        /* ops for this behavior */
  97         struct bhv_desc *bd_next;       /* next behavior in chain */
  98 } bhv_desc_t;
  99
 100 /*
 101  * Behavior identity field.  A behavior's identity determines the position
 102  * where it lives within a behavior chain, and it's always the first field
 103  * of the behavior's ops vector. The optional id field further identifies the
 104  * subsystem responsible for the behavior.
 105  */
 106 typedef struct bhv_identity {
 107         __u16   bi_id;          /* owning subsystem id */
 108         __u16   bi_position;    /* position in chain */
 109 } bhv_identity_t;
 110
 111 typedef bhv_identity_t bhv_position_t;
 112
 113 #define BHV_IDENTITY_INIT(id,pos)       {id, pos}
 114 #define BHV_IDENTITY_INIT_POSITION(pos) BHV_IDENTITY_INIT(0, pos)
 115
 116 /*
 117  * Define boundaries of position values.
 118  */
 119 #define BHV_POSITION_INVALID    0       /* invalid position number */
 120 #define BHV_POSITION_BASE       1       /* base (last) implementation layer */
 121 #define BHV_POSITION_TOP        63      /* top (first) implementation layer */
 122
 123 /*
 124  * Plumbing macros.
 125  */
 126 #define BHV_HEAD_FIRST(bhp)     (ASSERT((bhp)->bh_first), (bhp)->bh_first)
 127 #define BHV_NEXT(bdp)           (ASSERT((bdp)->bd_next), (bdp)->bd_next)
 128 #define BHV_NEXTNULL(bdp)       ((bdp)->bd_next)
 129 #define BHV_VOBJ(bdp)           (ASSERT((bdp)->bd_vobj), (bdp)->bd_vobj)
 130 #define BHV_VOBJNULL(bdp)       ((bdp)->bd_vobj)
 131 #define BHV_PDATA(bdp)          (bdp)->bd_pdata
 132 #define BHV_OPS(bdp)            (bdp)->bd_ops
 133 #define BHV_IDENTITY(bdp)       ((bhv_identity_t *)(bdp)->bd_ops)
 134 #define BHV_POSITION(bdp)       (BHV_IDENTITY(bdp)->bi_position)
 135
 136 extern void bhv_head_init(bhv_head_t *, char *);
 137 extern void bhv_head_destroy(bhv_head_t *);
 138 extern int  bhv_insert(bhv_head_t *, bhv_desc_t *);
 139 extern void bhv_insert_initial(bhv_head_t *, bhv_desc_t *);
 140
 141 /*
 142  * Initialize a new behavior descriptor.
 143  * Arguments:
 144  *   bdp - pointer to behavior descriptor
 145  *   pdata - pointer to behavior's private data
 146  *   vobj - pointer to associated virtual object
 147  *   ops - pointer to ops for this behavior
 148  */
 149 #define bhv_desc_init(bdp, pdata, vobj, ops)            \
 150  {                                                      \
 151         (bdp)->bd_pdata = pdata;                        \
 152         (bdp)->bd_vobj = vobj;                          \
 153         (bdp)->bd_ops = ops;                            \
 154         (bdp)->bd_next = NULL;                          \
 155  }
 156
 157 /*
 158  * Remove a behavior descriptor from a behavior chain.
 159  */
 160 #define bhv_remove(bhp, bdp)                            \
 161  {                                                      \
 162         if ((bhp)->bh_first == (bdp)) {                 \
 163                 /*                                      \
 164                 * Remove from front of chain.           \
 165                 * Atomic wrt oip's.                     \
 166                 */                                      \
 167                (bhp)->bh_first = (bdp)->bd_next;        \
 168         } else {                                        \
 169                /* remove from non-front of chain */     \
 170                bhv_remove_not_first(bhp, bdp);          \
 171         }                                               \
 172         (bdp)->bd_vobj = NULL;                          \
 173  }
 174
 175 /*
 176  * Behavior module prototypes.
 177  */
 178 extern void             bhv_remove_not_first(bhv_head_t *bhp, bhv_desc_t *bdp);
 179 extern bhv_desc_t *     bhv_lookup(bhv_head_t *bhp, void *ops);
 180 extern bhv_desc_t *     bhv_lookup_range(bhv_head_t *bhp, int low, int high);
 181 extern bhv_desc_t *     bhv_base(bhv_head_t *bhp);
 182
 183 /* No bhv locking on Linux */
 184 #define bhv_lookup_unlocked     bhv_lookup
 185 #define bhv_base_unlocked       bhv_base
 186
 187 #endif /* __XFS_BEHAVIOR_H__ */