include/linux/idr.h

/*
 * include/linux/idr.h
 * 
 * 2002-10-18  written by Jim Houston jim.houston@ccur.com
 *	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>

/*
 * Using 6 bits at each layer allows us to allocate 7 layers out of each page.
 * 8 bits only gave us 3 layers out of every pair of pages, which is less
 * efficient except for trees with a largest element between 192-255 inclusive.
 */
#define IDR_BITS 6
#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" */
		DECLARE_BITMAP(bitmap, IDR_SIZE);
		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)

/**
 * idr_get_cursor - Return the current position of the cyclic allocator
 * @idr: idr handle
 *
 * The value returned is the value that will be next returned from
 * idr_alloc_cyclic() if it is free (otherwise the search will start from
 * this position).
 */
static inline unsigned int idr_get_cursor(struct idr *idr)
{
	return READ_ONCE(idr->cur);
}

/**
 * idr_set_cursor - Set the current position of the cyclic allocator
 * @idr: idr handle
 * @val: new position
 *
 * The next call to idr_alloc_cyclic() will return @val if it is free
 * (otherwise the search will start from this position).
 */
static inline void idr_set_cursor(struct idr *idr, unsigned int val)
{
	WRITE_ONCE(idr->cur, val);
}

/**
 * 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)
{
	preempt_enable();
}

/**
 * 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)

/**
 * idr_for_each_entry - continue iteration over an idr's elements of a given type
 * @idp:     idr handle
 * @entry:   the type * to use as cursor
 * @id:      id entry's key
 *
 * Continue to iterate over list of given type, continuing after
 * the current position.
 */
#define idr_for_each_entry_continue(idp, entry, id)			\
	for ((entry) = idr_get_next((idp), &(id));			\
	     entry;							\
	     ++id, (entry) = idr_get_next((idp), &(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);
}

static inline bool ida_is_empty(struct ida *ida)
{
	return idr_is_empty(&ida->idr);
}

void __init idr_init_cache(void);

#endif /* __IDR_H__ */