/*
 * em_canid.c  Ematch rule to match CAN frames according to their CAN IDs
 *
 *              This program is free software; you can distribute it and/or
 *              modify it under the terms of the GNU General Public License
 *              as published by the Free Software Foundation; either version
 *              2 of the License, or (at your option) any later version.
 *
 * Idea:       Oliver Hartkopp <oliver.hartkopp@volkswagen.de>
 * Copyright:  (c) 2011 Czech Technical University in Prague
 *             (c) 2011 Volkswagen Group Research
 * Authors:    Michal Sojka <sojkam1@fel.cvut.cz>
 *             Pavel Pisa <pisa@cmp.felk.cvut.cz>
 *             Rostislav Lisovy <lisovy@gmail.cz>
 * Funded by:  Volkswagen Group Research
 */

#include <linux/slab.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/skbuff.h>
#include <net/pkt_cls.h>
#include <linux/can.h>

#define EM_CAN_RULES_MAX 500

struct canid_match {
        /* For each SFF CAN ID (11 bit) there is one record in this bitfield */
        DECLARE_BITMAP(match_sff, (1 << CAN_SFF_ID_BITS));

        int rules_count;
        int sff_rules_count;
        int eff_rules_count;

        /*
         * Raw rules copied from netlink message; Used for sending
         * information to userspace (when 'tc filter show' is invoked)
         * AND when matching EFF frames
         */
        struct can_filter rules_raw[];
};

/**
 * em_canid_get_id() - Extracts Can ID out of the sk_buff structure.
 */
static canid_t em_canid_get_id(struct sk_buff *skb)
{
        /* CAN ID is stored within the data field */
        struct can_frame *cf = (struct can_frame *)skb->data;

        return cf->can_id;
}

static void em_canid_sff_match_add(struct canid_match *cm, u32 can_id,
                                        u32 can_mask)
{
        int i;

        /*
         * Limit can_mask and can_id to SFF range to
         * protect against write after end of array
         */
        can_mask &= CAN_SFF_MASK;
        can_id &= can_mask;

        /* Single frame */
        if (can_mask == CAN_SFF_MASK) {
                set_bit(can_id, cm->match_sff);
                return;
        }

        /* All frames */
        if (can_mask == 0) {
                bitmap_fill(cm->match_sff, (1 << CAN_SFF_ID_BITS));
                return;
        }

        /*
         * Individual frame filter.
         * Add record (set bit to 1) for each ID that
         * conforms particular rule
         */
        for (i = 0; i < (1 << CAN_SFF_ID_BITS); i++) {
                if ((i & can_mask) == can_id)
                        set_bit(i, cm->match_sff);
        }
}

static inline struct canid_match *em_canid_priv(struct tcf_ematch *m)
{
        return (struct canid_match *)m->data;
}

static int em_canid_match(struct sk_buff *skb, struct tcf_ematch *m,
                         struct tcf_pkt_info *info)
{
        struct canid_match *cm = em_canid_priv(m);
        canid_t can_id;
        int match = 0;
        int i;
        const struct can_filter *lp;

        can_id = em_canid_get_id(skb);

        if (can_id & CAN_EFF_FLAG) {
                for (i = 0, lp = cm->rules_raw;
                     i < cm->eff_rules_count; i++, lp++) {
                        if (!(((lp->can_id ^ can_id) & lp->can_mask))) {
                                match = 1;
                                break;
                        }
                }
        } else { /* SFF */
                can_id &= CAN_SFF_MASK;
                match = (test_bit(can_id, cm->match_sff) ? 1 : 0);
        }

        return match;
}

static int em_canid_change(struct tcf_proto *tp, void *data, int len,
                          struct tcf_ematch *m)
{
        struct can_filter *conf = data; /* Array with rules */
        struct canid_match *cm;
        struct canid_match *cm_old = (struct canid_match *)m->data;
        int i;

        if (!len)
                return -EINVAL;

        if (len % sizeof(struct can_filter))
                return -EINVAL;

        if (len > sizeof(struct can_filter) * EM_CAN_RULES_MAX)
                return -EINVAL;

        cm = kzalloc(sizeof(struct canid_match) + len, GFP_KERNEL);
        if (!cm)
                return -ENOMEM;

        cm->rules_count = len / sizeof(struct can_filter);

        /*
         * We need two for() loops for copying rules into two contiguous
         * areas in rules_raw to process all eff rules with a simple loop.
         * NB: The configuration interface supports sff and eff rules.
         * We do not support filters here that match for the same can_id
         * provided in a SFF and EFF frame (e.g. 0x123 / 0x80000123).
         * For this (unusual case) two filters have to be specified. The
         * SFF/EFF separation is done with the CAN_EFF_FLAG in the can_id.
         */

        /* Fill rules_raw with EFF rules first */
        for (i = 0; i < cm->rules_count; i++) {
                if (conf[i].can_id & CAN_EFF_FLAG) {
                        memcpy(cm->rules_raw + cm->eff_rules_count,
                                &conf[i],
                                sizeof(struct can_filter));

                        cm->eff_rules_count++;
                }
        }

        /* append SFF frame rules */
        for (i = 0; i < cm->rules_count; i++) {
                if (!(conf[i].can_id & CAN_EFF_FLAG)) {
                        memcpy(cm->rules_raw
                                + cm->eff_rules_count
                                + cm->sff_rules_count,
                                &conf[i], sizeof(struct can_filter));

                        cm->sff_rules_count++;

                        em_canid_sff_match_add(cm,
                                conf[i].can_id, conf[i].can_mask);
                }
        }

        m->datalen = sizeof(struct canid_match) + len;
        m->data = (unsigned long)cm;

        if (cm_old != NULL) {
                pr_err("canid: Configuring an existing ematch!\n");
                kfree(cm_old);
        }

        return 0;
}

static void em_canid_destroy(struct tcf_proto *tp, struct tcf_ematch *m)
{
        struct canid_match *cm = em_canid_priv(m);

        kfree(cm);
}

static int em_canid_dump(struct sk_buff *skb, struct tcf_ematch *m)
{
        struct canid_match *cm = em_canid_priv(m);

        /*
         * When configuring this ematch 'rules_count' is set not to exceed
         * 'rules_raw' array size
         */
        if (nla_put_nohdr(skb, sizeof(struct can_filter) * cm->rules_count,
            &cm->rules_raw) < 0)
                return -EMSGSIZE;

        return 0;
}

static struct tcf_ematch_ops em_canid_ops = {
        .kind     = TCF_EM_CANID,
        .change   = em_canid_change,
        .match    = em_canid_match,
        .destroy  = em_canid_destroy,
        .dump     = em_canid_dump,
        .owner    = THIS_MODULE,
        .link     = LIST_HEAD_INIT(em_canid_ops.link)
};

static int __init init_em_canid(void)
{
        return tcf_em_register(&em_canid_ops);
}

static void __exit exit_em_canid(void)
{
        tcf_em_unregister(&em_canid_ops);
}

MODULE_LICENSE("GPL");

module_init(init_em_canid);
module_exit(exit_em_canid);

MODULE_ALIAS_TCF_EMATCH(TCF_EM_CANID);