id_table.c

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/*
 * Copyright (c) 2011 Chelsio Communications.  All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - 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.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
#include <linux/kernel.h>
#include <linux/random.h>
#include "iw_cxgb4.h"

#define RANDOM_SKIP 16

/*
 * Trivial bitmap-based allocator. If the random flag is set, the
 * allocator is designed to:
 * - pseudo-randomize the id returned such that it is not trivially predictable.
 * - avoid reuse of recently used id (at the expense of predictability)
 */
u32 c4iw_id_alloc(struct c4iw_id_table *alloc)
{
    unsigned long flags;
    u32 obj;

    spin_lock_irqsave(&alloc->lock, flags);

    obj = find_next_zero_bit(alloc->table, alloc->max, alloc->last);
    if (obj >= alloc->max)
        obj = find_first_zero_bit(alloc->table, alloc->max);

    if (obj < alloc->max) {
        if (alloc->flags & C4IW_ID_TABLE_F_RANDOM)
            alloc->last += random32() % RANDOM_SKIP;
        else
            alloc->last = obj + 1;
        if (alloc->last >= alloc->max)
            alloc->last = 0;
        set_bit(obj, alloc->table);
        obj += alloc->start;
    } else
        obj = -1;

    spin_unlock_irqrestore(&alloc->lock, flags);
    return obj;
}

void c4iw_id_free(struct c4iw_id_table *alloc, u32 obj)
{
    unsigned long flags;

    obj -= alloc->start;
    BUG_ON((int)obj < 0);

    spin_lock_irqsave(&alloc->lock, flags);
    clear_bit(obj, alloc->table);
    spin_unlock_irqrestore(&alloc->lock, flags);
}

int c4iw_id_table_alloc(struct c4iw_id_table *alloc, u32 start, u32 num,
            u32 reserved, u32 flags)
{
    int i;

    alloc->start = start;
    alloc->flags = flags;
    if (flags & C4IW_ID_TABLE_F_RANDOM)
        alloc->last = random32() % RANDOM_SKIP;
    else
        alloc->last = 0;
    alloc->max  = num;
    spin_lock_init(&alloc->lock);
    alloc->table = kmalloc(BITS_TO_LONGS(num) * sizeof(long),
                GFP_KERNEL);
    if (!alloc->table)
        return -ENOMEM;

    bitmap_zero(alloc->table, num);
    if (!(alloc->flags & C4IW_ID_TABLE_F_EMPTY))
        for (i = 0; i < reserved; ++i)
            set_bit(i, alloc->table);

    return 0;
}

void c4iw_id_table_free(struct c4iw_id_table *alloc)
{
    kfree(alloc->table);
}