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Linux/include/linux/idr.h

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  1 /*
  2  * include/linux/idr.h
  3  * 
  4  * 2002-10-18  written by Jim Houston jim.houston@ccur.com
  5  *      Copyright (C) 2002 by Concurrent Computer Corporation
  6  *      Distributed under the GNU GPL license version 2.
  7  *
  8  * Small id to pointer translation service avoiding fixed sized
  9  * tables.
 10  */
 11 
 12 #ifndef __IDR_H__
 13 #define __IDR_H__
 14 
 15 #include <linux/types.h>
 16 #include <linux/bitops.h>
 17 #include <linux/init.h>
 18 #include <linux/rcupdate.h>
 19 
 20 /*
 21  * We want shallower trees and thus more bits covered at each layer.  8
 22  * bits gives us large enough first layer for most use cases and maximum
 23  * tree depth of 4.  Each idr_layer is slightly larger than 2k on 64bit and
 24  * 1k on 32bit.
 25  */
 26 #define IDR_BITS 8
 27 #define IDR_SIZE (1 << IDR_BITS)
 28 #define IDR_MASK ((1 << IDR_BITS)-1)
 29 
 30 struct idr_layer {
 31         int                     prefix; /* the ID prefix of this idr_layer */
 32         int                     layer;  /* distance from leaf */
 33         struct idr_layer __rcu  *ary[1<<IDR_BITS];
 34         int                     count;  /* When zero, we can release it */
 35         union {
 36                 /* A zero bit means "space here" */
 37                 DECLARE_BITMAP(bitmap, IDR_SIZE);
 38                 struct rcu_head         rcu_head;
 39         };
 40 };
 41 
 42 struct idr {
 43         struct idr_layer __rcu  *hint;  /* the last layer allocated from */
 44         struct idr_layer __rcu  *top;
 45         int                     layers; /* only valid w/o concurrent changes */
 46         int                     cur;    /* current pos for cyclic allocation */
 47         spinlock_t              lock;
 48         int                     id_free_cnt;
 49         struct idr_layer        *id_free;
 50 };
 51 
 52 #define IDR_INIT(name)                                                  \
 53 {                                                                       \
 54         .lock                   = __SPIN_LOCK_UNLOCKED(name.lock),      \
 55 }
 56 #define DEFINE_IDR(name)        struct idr name = IDR_INIT(name)
 57 
 58 /**
 59  * DOC: idr sync
 60  * idr synchronization (stolen from radix-tree.h)
 61  *
 62  * idr_find() is able to be called locklessly, using RCU. The caller must
 63  * ensure calls to this function are made within rcu_read_lock() regions.
 64  * Other readers (lock-free or otherwise) and modifications may be running
 65  * concurrently.
 66  *
 67  * It is still required that the caller manage the synchronization and
 68  * lifetimes of the items. So if RCU lock-free lookups are used, typically
 69  * this would mean that the items have their own locks, or are amenable to
 70  * lock-free access; and that the items are freed by RCU (or only freed after
 71  * having been deleted from the idr tree *and* a synchronize_rcu() grace
 72  * period).
 73  */
 74 
 75 /*
 76  * This is what we export.
 77  */
 78 
 79 void *idr_find_slowpath(struct idr *idp, int id);
 80 void idr_preload(gfp_t gfp_mask);
 81 int idr_alloc(struct idr *idp, void *ptr, int start, int end, gfp_t gfp_mask);
 82 int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask);
 83 int idr_for_each(struct idr *idp,
 84                  int (*fn)(int id, void *p, void *data), void *data);
 85 void *idr_get_next(struct idr *idp, int *nextid);
 86 void *idr_replace(struct idr *idp, void *ptr, int id);
 87 void idr_remove(struct idr *idp, int id);
 88 void idr_destroy(struct idr *idp);
 89 void idr_init(struct idr *idp);
 90 bool idr_is_empty(struct idr *idp);
 91 
 92 /**
 93  * idr_preload_end - end preload section started with idr_preload()
 94  *
 95  * Each idr_preload() should be matched with an invocation of this
 96  * function.  See idr_preload() for details.
 97  */
 98 static inline void idr_preload_end(void)
 99 {
100         preempt_enable();
101 }
102 
103 /**
104  * idr_find - return pointer for given id
105  * @idr: idr handle
106  * @id: lookup key
107  *
108  * Return the pointer given the id it has been registered with.  A %NULL
109  * return indicates that @id is not valid or you passed %NULL in
110  * idr_get_new().
111  *
112  * This function can be called under rcu_read_lock(), given that the leaf
113  * pointers lifetimes are correctly managed.
114  */
115 static inline void *idr_find(struct idr *idr, int id)
116 {
117         struct idr_layer *hint = rcu_dereference_raw(idr->hint);
118 
119         if (hint && (id & ~IDR_MASK) == hint->prefix)
120                 return rcu_dereference_raw(hint->ary[id & IDR_MASK]);
121 
122         return idr_find_slowpath(idr, id);
123 }
124 
125 /**
126  * idr_for_each_entry - iterate over an idr's elements of a given type
127  * @idp:     idr handle
128  * @entry:   the type * to use as cursor
129  * @id:      id entry's key
130  *
131  * @entry and @id do not need to be initialized before the loop, and
132  * after normal terminatinon @entry is left with the value NULL.  This
133  * is convenient for a "not found" value.
134  */
135 #define idr_for_each_entry(idp, entry, id)                      \
136         for (id = 0; ((entry) = idr_get_next(idp, &(id))) != NULL; ++id)
137 
138 /*
139  * IDA - IDR based id allocator, use when translation from id to
140  * pointer isn't necessary.
141  *
142  * IDA_BITMAP_LONGS is calculated to be one less to accommodate
143  * ida_bitmap->nr_busy so that the whole struct fits in 128 bytes.
144  */
145 #define IDA_CHUNK_SIZE          128     /* 128 bytes per chunk */
146 #define IDA_BITMAP_LONGS        (IDA_CHUNK_SIZE / sizeof(long) - 1)
147 #define IDA_BITMAP_BITS         (IDA_BITMAP_LONGS * sizeof(long) * 8)
148 
149 struct ida_bitmap {
150         long                    nr_busy;
151         unsigned long           bitmap[IDA_BITMAP_LONGS];
152 };
153 
154 struct ida {
155         struct idr              idr;
156         struct ida_bitmap       *free_bitmap;
157 };
158 
159 #define IDA_INIT(name)          { .idr = IDR_INIT((name).idr), .free_bitmap = NULL, }
160 #define DEFINE_IDA(name)        struct ida name = IDA_INIT(name)
161 
162 int ida_pre_get(struct ida *ida, gfp_t gfp_mask);
163 int ida_get_new_above(struct ida *ida, int starting_id, int *p_id);
164 void ida_remove(struct ida *ida, int id);
165 void ida_destroy(struct ida *ida);
166 void ida_init(struct ida *ida);
167 
168 int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
169                    gfp_t gfp_mask);
170 void ida_simple_remove(struct ida *ida, unsigned int id);
171 
172 /**
173  * ida_get_new - allocate new ID
174  * @ida:        idr handle
175  * @p_id:       pointer to the allocated handle
176  *
177  * Simple wrapper around ida_get_new_above() w/ @starting_id of zero.
178  */
179 static inline int ida_get_new(struct ida *ida, int *p_id)
180 {
181         return ida_get_new_above(ida, 0, p_id);
182 }
183 
184 void __init idr_init_cache(void);
185 
186 #endif /* __IDR_H__ */
187 

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