list_bl.h

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#ifndef _LINUX_LIST_BL_H
#define _LINUX_LIST_BL_H

#include <linux/list.h>
#include <linux/bit_spinlock.h>

/*
 * Special version of lists, where head of the list has a lock in the lowest
 * bit. This is useful for scalable hash tables without increasing memory
 * footprint overhead.
 *
 * For modification operations, the 0 bit of hlist_bl_head->first
 * pointer must be set.
 *
 * With some small modifications, this can easily be adapted to store several
 * arbitrary bits (not just a single lock bit), if the need arises to store
 * some fast and compact auxiliary data.
 */

#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
#define LIST_BL_LOCKMASK    1UL
#else
#define LIST_BL_LOCKMASK    0UL
#endif

#ifdef CONFIG_DEBUG_LIST
#define LIST_BL_BUG_ON(x) BUG_ON(x)
#else
#define LIST_BL_BUG_ON(x)
#endif


struct hlist_bl_head {
    struct hlist_bl_node *first;
};

struct hlist_bl_node {
    struct hlist_bl_node *next, **pprev;
};
#define INIT_HLIST_BL_HEAD(ptr) \
    ((ptr)->first = NULL)

static inline void INIT_HLIST_BL_NODE(struct hlist_bl_node *h)
{
    h->next = NULL;
    h->pprev = NULL;
}

#define hlist_bl_entry(ptr, type, member) container_of(ptr,type,member)

static inline int hlist_bl_unhashed(const struct hlist_bl_node *h)
{
    return !h->pprev;
}

static inline struct hlist_bl_node *hlist_bl_first(struct hlist_bl_head *h)
{
    return (struct hlist_bl_node *)
        ((unsigned long)h->first & ~LIST_BL_LOCKMASK);
}

static inline void hlist_bl_set_first(struct hlist_bl_head *h,
                    struct hlist_bl_node *n)
{
    LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
    LIST_BL_BUG_ON(((unsigned long)h->first & LIST_BL_LOCKMASK) !=
                            LIST_BL_LOCKMASK);
    h->first = (struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK);
}

static inline int hlist_bl_empty(const struct hlist_bl_head *h)
{
    return !((unsigned long)h->first & ~LIST_BL_LOCKMASK);
}

static inline void hlist_bl_add_head(struct hlist_bl_node *n,
                    struct hlist_bl_head *h)
{
    struct hlist_bl_node *first = hlist_bl_first(h);

    n->next = first;
    if (first)
        first->pprev = &n->next;
    n->pprev = &h->first;
    hlist_bl_set_first(h, n);
}

static inline void __hlist_bl_del(struct hlist_bl_node *n)
{
    struct hlist_bl_node *next = n->next;
    struct hlist_bl_node **pprev = n->pprev;

    LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);

    /* pprev may be `first`, so be careful not to lose the lock bit */
    *pprev = (struct hlist_bl_node *)
            ((unsigned long)next |
             ((unsigned long)*pprev & LIST_BL_LOCKMASK));
    if (next)
        next->pprev = pprev;
}

static inline void hlist_bl_del(struct hlist_bl_node *n)
{
    __hlist_bl_del(n);
    n->next = LIST_POISON1;
    n->pprev = LIST_POISON2;
}

static inline void hlist_bl_del_init(struct hlist_bl_node *n)
{
    if (!hlist_bl_unhashed(n)) {
        __hlist_bl_del(n);
        INIT_HLIST_BL_NODE(n);
    }
}

static inline void hlist_bl_lock(struct hlist_bl_head *b)
{
    bit_spin_lock(0, (unsigned long *)b);
}

static inline void hlist_bl_unlock(struct hlist_bl_head *b)
{
    __bit_spin_unlock(0, (unsigned long *)b);
}

#define hlist_bl_for_each_entry(tpos, pos, head, member)        \
    for (pos = hlist_bl_first(head);                \
         pos &&                         \
        ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1;}); \
         pos = pos->next)

#define hlist_bl_for_each_entry_safe(tpos, pos, n, head, member)     \
    for (pos = hlist_bl_first(head);                 \
         pos && ({ n = pos->next; 1; }) &&               \
        ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1;}); \
         pos = n)

#endif