path: root/lib/idr.c

/*
 * 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.
 *
 * Modified by George Anzinger to reuse immediately and to use
 * find bit instructions.  Also removed _irq on spinlocks.
 *
 * Modified by Nadia Derbey to make it RCU safe.
 *
 * Small id to pointer translation service.
 *
 * It uses a radix tree like structure as a sparse array indexed
 * by the id to obtain the pointer.  The bitmap makes allocating
 * a new id quick.
 *
 * You call it to allocate an id (an int) an associate with that id a
 * pointer or what ever, we treat it as a (void *).  You can pass this
 * id to a user for him to pass back at a later time.  You then pass
 * that id to this code and it returns your pointer.
 */

#ifndef TEST                        // to test in user space...
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/export.h>
#endif
#include <linux/err.h>
#include <linux/string.h>
#include <linux/idr.h>
#include <linux/spinlock.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>

#define MAX_IDR_SHIFT		(sizeof(int) * 8 - 1)
#define MAX_IDR_BIT		(1U << MAX_IDR_SHIFT)

/* Leave the possibility of an incomplete final layer */
#define MAX_IDR_LEVEL ((MAX_IDR_SHIFT + IDR_BITS - 1) / IDR_BITS)

/* Number of id_layer structs to leave in free list */
#define MAX_IDR_FREE (MAX_IDR_LEVEL * 2)

static struct kmem_cache *idr_layer_cache;
static DEFINE_PER_CPU(struct idr_layer *, idr_preload_head);
static DEFINE_PER_CPU(int, idr_preload_cnt);
static DEFINE_SPINLOCK(simple_ida_lock);

/* the maximum ID which can be allocated given idr->layers */
static int idr_max(int layers)
{
	int bits = min_t(int, layers * IDR_BITS, MAX_IDR_SHIFT);

	return (1 << bits) - 1;
}

/*
 * Prefix mask for an idr_layer at @layer.  For layer 0, the prefix mask is
 * all bits except for the lower IDR_BITS.  For layer 1, 2 * IDR_BITS, and
 * so on.
 */
static int idr_layer_prefix_mask(int layer)
{
	return ~idr_max(layer + 1);
}

static struct idr_layer *get_from_free_list(struct idr *idp)
{
	struct idr_layer *p;
	unsigned long flags;

	spin_lock_irqsave(&idp->lock, flags);
	if ((p = idp->id_free)) {
		idp->id_free = p->ary[0];
		idp->id_free_cnt--;
		p->ary[0] = NULL;
	}
	spin_unlock_irqrestore(&idp->lock, flags);
	return(p);
}

/**
 * idr_layer_alloc - allocate a new idr_layer
 * @gfp_mask: allocation mask
 * @layer_idr: optional idr to allocate from
 *
 * If @layer_idr is %NULL, directly allocate one using @gfp_mask or fetch
 * one from the per-cpu preload buffer.  If @layer_idr is not %NULL, fetch
 * an idr_layer from @idr->id_free.
 *
 * @layer_idr is to maintain backward compatibility with the old alloc
 * interface - idr_pre_get() and idr_get_new*() - and will be removed
 * together with per-pool preload buffer.
 */
static struct idr_layer *idr_layer_alloc(gfp_t gfp_mask, struct idr *layer_idr)
{
	struct idr_layer *new;

	/* this is the old path, bypass to get_from_free_list() */
	if (layer_idr)
		return get_from_free_list(layer_idr);

	/*
	 * Try to allocate directly from kmem_cache.  We want to try this
	 * before preload buffer; otherwise, non-preloading idr_alloc()
	 * users will end up taking advantage of preloading ones.  As the
	 * following is allowed to fail for preloaded cases, suppress
	 * warning this time.
	 */
	new = kmem_cache_zalloc(idr_layer_cache, gfp_mask | __GFP_NOWARN);
	if (new)
		return new;

	/*
	 * Try to fetch one from the per-cpu preload buffer if in process
	 * context.  See idr_preload() for details.
	 */
	if (!in_interrupt()) {
		preempt_disable();
		new = __this_cpu_read(idr_preload_head);
		if (new) {
			__this_cpu_write(idr_preload_head, new->ary[0]);
			__this_cpu_dec(idr_preload_cnt);
			new->ary[0] = NULL;
		}
		preempt_enable();
		if (new)
			return new;
	}

	/*
	 * Both failed.  Try kmem_cache again w/o adding __GFP_NOWARN so
	 * that memory allocation failure warning is printed as intended.
	 */
	return kmem_cache_zalloc(idr_layer_cache, gfp_mask);
}

static void idr_layer_rcu_free(struct rcu_head *head)
{
	struct idr_layer *layer;

	layer = container_of(head, struct idr_layer, rcu_head);
	kmem_cache_free(idr_layer_cache, layer);
}

static inline void free_layer(struct idr *idr, struct idr_layer *p)
{
	if (idr->hint == p)
		RCU_INIT_POINTER(idr->hint, NULL);
	call_rcu(&p->rcu_head, idr_layer_rcu_free)