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* include/linux/idr.h
* 2002-10-18 written by Jim Houston
* Copyright (C) 2002 by Concurrent Computer Corporation
* Distributed under the GNU GPL license version 2.
* Small id to pointer translation service avoiding fixed sized
* tables.
#ifndef __IDR_H__
#define __IDR_H__
#include <linux/types.h>
#include <linux/bitops.h>
#include <linux/init.h>
#include <linux/rcupdate.h>
* We want shallower trees and thus more bits covered at each layer. 8
* bits gives us large enough first layer for most use cases and maximum
* tree depth of 4. Each idr_layer is slightly larger than 2k on 64bit and
* 1k on 32bit.
#define IDR_BITS 8
#define IDR_SIZE (1 << IDR_BITS)
#define IDR_MASK ((1 << IDR_BITS)-1)
struct idr_layer {
int prefix; /* the ID prefix of this idr_layer */
int layer; /* distance from leaf */
struct idr_layer __rcu *ary[1<<IDR_BITS];
int count; /* When zero, we can release it */
union {
/* A zero bit means "space here" */
struct rcu_head rcu_head;
struct idr {
struct idr_layer __rcu *hint; /* the last layer allocated from */
struct idr_layer __rcu *top;
int layers; /* only valid w/o concurrent changes */
int cur; /* current pos for cyclic allocation */
spinlock_t lock;
int id_free_cnt;
struct idr_layer *id_free;
#define IDR_INIT(name) \
{ \
.lock = __SPIN_LOCK_UNLOCKED(name.lock), \
#define DEFINE_IDR(name) struct idr name = IDR_INIT(name)
* DOC: idr sync
* idr synchronization (stolen from radix-tree.h)
* idr_find() is able to be called locklessly, using RCU. The caller must
* ensure calls to this function are made within rcu_read_lock() regions.
* Other readers (lock-free or otherwise) and modifications may be running
* concurrently.
* It is still required that the caller manage the synchronization and
* lifetimes of the items. So if RCU lock-free lookups are used, typically
* this would mean that the items have their own locks, or are amenable to
* lock-free access; and that the items are freed by RCU (or only freed after
* having been deleted from the idr tree *and* a synchronize_rcu() grace
* period).
* This is what we export.
void *idr_find_slowpath(struct idr *idp, int id);
void idr_preload(gfp_t gfp_mask);
int idr_alloc(struct idr *idp, void *ptr, int start, int end, gfp_t gfp_mask);
int idr_alloc_cyclic(struct idr *idr, void *ptr, int start, int end, gfp_t gfp_mask);
int idr_for_each(struct idr *idp,
int (*fn)(int id, void *p, void *data), void *data);
void *idr_get_next(struct idr *idp, int *nextid);
void *idr_replace(struct idr *idp, void *ptr, int id);
void idr_remove(struct idr *idp, int id);
void idr_destroy(struct idr *idp);
void idr_init(struct idr *idp);
bool idr_is_empty(struct idr *idp);
* idr_preload_end - end preload section started with idr_preload()
* Each idr_preload() should be matched with an invocation of this
* function. See idr_preload() for details.
static inline void idr_preload_end(void)
* idr_find - return pointer for given id
* @idr: idr handle
* @id: lookup key
* Return the pointer given the id it has been registered with. A %NULL
* return indicates that @id is not valid or you passed %NULL in
* idr_get_new().
* This function can be called under rcu_read_lock(), given that the leaf
* pointers lifetimes are correctly managed.
static inline void *idr_find(struct idr *idr, int id)
struct idr_layer *hint = rcu_dereference_raw(idr->hint);
if (hint && (id & ~IDR_MASK) == hint->prefix)
return rcu_dereference_raw(hint->ary[id & IDR_MASK]);
return idr_find_slowpath(idr, id);
* idr_for_each_entry - iterate over an idr's elements of a given type
* @idp: idr handle
* @entry: the type * to use as cursor
* @id: id entry's key
* @entry and @id do not need to be initialized before the loop, and
* after normal terminatinon @entry is left with the value NULL. This
* is convenient for a "not found" value.
#define idr_for_each_entry(idp, entry, id) \
for (id = 0; ((entry) = idr_get_next(idp, &(id))) != NULL; ++id)
* IDA - IDR based id allocator, use when translation from id to
* pointer isn't necessary.
* IDA_BITMAP_LONGS is calculated to be one less to accommodate
* ida_bitmap->nr_busy so that the whole struct fits in 128 bytes.
#define IDA_CHUNK_SIZE 128 /* 128 bytes per chunk */
#define IDA_BITMAP_LONGS (IDA_CHUNK_SIZE / sizeof(long) - 1)
#define IDA_BITMAP_BITS (IDA_BITMAP_LONGS * sizeof(long) * 8)
struct ida_bitmap {
long nr_busy;
unsigned long bitmap[IDA_BITMAP_LONGS];
struct ida {
struct idr idr;
struct ida_bitmap *free_bitmap;
#define IDA_INIT(name) { .idr = IDR_INIT((name).idr), .free_bitmap = NULL, }
#define DEFINE_IDA(name) struct ida name = IDA_INIT(name)
int ida_pre_get(struct ida *ida, gfp_t gfp_mask);
int ida_get_new_above(struct ida *ida, int starting_id, int *p_id);
void ida_remove(struct ida *ida, int id);
void ida_destroy(struct ida *ida);
void ida_init(struct ida *ida);
int ida_simple_get(struct ida *ida, unsigned int start, unsigned int end,
gfp_t gfp_mask);
void ida_simple_remove(struct ida *ida, unsigned int id);
* ida_get_new - allocate new ID
* @ida: idr handle
* @p_id: pointer to the allocated handle
* Simple wrapper around ida_get_new_above() w/ @starting_id of zero.
static inline int ida_get_new(struct ida *ida, int *p_id)
return ida_get_new_above(ida, 0, p_id);
void __init idr_init_cache(void);
#endif /* __IDR_H__ */