ref.c

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/*
 * net/tipc/ref.c: TIPC object registry code
 *
 * Copyright (c) 1991-2006, Ericsson AB
 * Copyright (c) 2004-2007, Wind River Systems
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the names of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include "core.h"
#include "ref.h"

struct reference {
    void *object;
    spinlock_t lock;
    u32 ref;
};

struct ref_table {
    struct reference *entries;
    u32 capacity;
    u32 init_point;
    u32 first_free;
    u32 last_free;
    u32 index_mask;
    u32 start_mask;
};

/*
 * Object reference table consists of 2**N entries.
 *
 * State    Object ptr  Reference
 * -----        ----------      ---------
 * In use        non-NULL       XXXX|own index
 *              (XXXX changes each time entry is acquired)
 * Free            NULL         YYYY|next free index
 *              (YYYY is one more than last used XXXX)
 * Uninitialized   NULL         0
 *
 * Entry 0 is not used; this allows index 0 to denote the end of the free list.
 *
 * Note that a reference value of 0 does not necessarily indicate that an
 * entry is uninitialized, since the last entry in the free list could also
 * have a reference value of 0 (although this is unlikely).
 */

static struct ref_table tipc_ref_table;

static DEFINE_RWLOCK(ref_table_lock);

int tipc_ref_table_init(u32 requested_size, u32 start)
{
    struct reference *table;
    u32 actual_size;

    /* account for unused entry, then round up size to a power of 2 */

    requested_size++;
    for (actual_size = 16; actual_size < requested_size; actual_size <<= 1)
        /* do nothing */ ;

    /* allocate table & mark all entries as uninitialized */
    table = vzalloc(actual_size * sizeof(struct reference));
    if (table == NULL)
        return -ENOMEM;

    tipc_ref_table.entries = table;
    tipc_ref_table.capacity = requested_size;
    tipc_ref_table.init_point = 1;
    tipc_ref_table.first_free = 0;
    tipc_ref_table.last_free = 0;
    tipc_ref_table.index_mask = actual_size - 1;
    tipc_ref_table.start_mask = start & ~tipc_ref_table.index_mask;

    return 0;
}

void tipc_ref_table_stop(void)
{
    if (!tipc_ref_table.entries)
        return;

    vfree(tipc_ref_table.entries);
    tipc_ref_table.entries = NULL;
}

u32 tipc_ref_acquire(void *object, spinlock_t **lock)
{
    u32 index;
    u32 index_mask;
    u32 next_plus_upper;
    u32 ref;
    struct reference *entry = NULL;

    if (!object) {
        pr_err("Attempt to acquire ref. to non-existent obj\n");
        return 0;
    }
    if (!tipc_ref_table.entries) {
        pr_err("Ref. table not found in acquisition attempt\n");
        return 0;
    }

    /* take a free entry, if available; otherwise initialize a new entry */
    write_lock_bh(&ref_table_lock);
    if (tipc_ref_table.first_free) {
        index = tipc_ref_table.first_free;
        entry = &(tipc_ref_table.entries[index]);
        index_mask = tipc_ref_table.index_mask;
        next_plus_upper = entry->ref;
        tipc_ref_table.first_free = next_plus_upper & index_mask;
        ref = (next_plus_upper & ~index_mask) + index;
    } else if (tipc_ref_table.init_point < tipc_ref_table.capacity) {
        index = tipc_ref_table.init_point++;
        entry = &(tipc_ref_table.entries[index]);
        spin_lock_init(&entry->lock);
        ref = tipc_ref_table.start_mask + index;
    } else {
        ref = 0;
    }
    write_unlock_bh(&ref_table_lock);

    /*
     * Grab the lock so no one else can modify this entry
     * While we assign its ref value & object pointer
     */
    if (entry) {
        spin_lock_bh(&entry->lock);
        entry->ref = ref;
        entry->object = object;
        *lock = &entry->lock;
        /*
         * keep it locked, the caller is responsible
         * for unlocking this when they're done with it
         */
    }

    return ref;
}

void tipc_ref_discard(u32 ref)
{
    struct reference *entry;
    u32 index;
    u32 index_mask;

    if (!tipc_ref_table.entries) {
        pr_err("Ref. table not found during discard attempt\n");
        return;
    }

    index_mask = tipc_ref_table.index_mask;
    index = ref & index_mask;
    entry = &(tipc_ref_table.entries[index]);

    write_lock_bh(&ref_table_lock);

    if (!entry->object) {
        pr_err("Attempt to discard ref. to non-existent obj\n");
        goto exit;
    }
    if (entry->ref != ref) {
        pr_err("Attempt to discard non-existent reference\n");
        goto exit;
    }

    /*
     * mark entry as unused; increment instance part of entry's reference
     * to invalidate any subsequent references
     */
    entry->object = NULL;
    entry->ref = (ref & ~index_mask) + (index_mask + 1);

    /* append entry to free entry list */
    if (tipc_ref_table.first_free == 0)
        tipc_ref_table.first_free = index;
    else
        tipc_ref_table.entries[tipc_ref_table.last_free].ref |= index;
    tipc_ref_table.last_free = index;

exit:
    write_unlock_bh(&ref_table_lock);
}

void *tipc_ref_lock(u32 ref)
{
    if (likely(tipc_ref_table.entries)) {
        struct reference *entry;

        entry = &tipc_ref_table.entries[ref &
                        tipc_ref_table.index_mask];
        if (likely(entry->ref != 0)) {
            spin_lock_bh(&entry->lock);
            if (likely((entry->ref == ref) && (entry->object)))
                return entry->object;
            spin_unlock_bh(&entry->lock);
        }
    }
    return NULL;
}


void *tipc_ref_deref(u32 ref)
{
    if (likely(tipc_ref_table.entries)) {
        struct reference *entry;

        entry = &tipc_ref_table.entries[ref &
                        tipc_ref_table.index_mask];
        if (likely(entry->ref == ref))
            return entry->object;
    }
    return NULL;
}