can-utils源码解析cansend

前言

本文主要介绍socketCan中的发送函数cansend的源码解析.

代码

/*
 * cansend.c - simple command line tool to send CAN-frames via CAN_RAW sockets
 *
 * Copyright (c) 2002-2007 Volkswagen Group Electronic Research
 * 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 name of Volkswagen nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * Alternatively, provided that this notice is retained in full, this
 * software may be distributed under the terms of the GNU General
 * Public License ("GPL") version 2, in which case the provisions of the
 * GPL apply INSTEAD OF those given above.
 *
 * The provided data structures and external interfaces from this code
 * are not restricted to be used by modules with a GPL compatible license.
 *
 * 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.
 *
 * Send feedback to <linux-can@vger.kernel.org>
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/socket.h>

#include <linux/can.h>
#include <linux/can/raw.h>

#include "lib.h"

int main( )
{
    int s; /* can raw socket */ 
    int required_mtu;
    int mtu;
    int enable_canfd = 1;
    struct sockaddr_can addr;
    struct canfd_frame frame;
    struct ifreq ifr;
    
    char* input = "008#abcd1234cdef567830";
    /* parse CAN frame */
    required_mtu = parse_canframe(input, &frame);
    printf("required_mtu is %d\n", required_mtu);
    printf("CAN_MTU is %d\n", (long unsigned int)CAN_MTU);
    //printf("CANID_DELIM is %d\n", CANID_DELIM);//#-35-0x23.
    printf("IFNAMSIZ is %d\n", IFNAMSIZ);
    if (!required_mtu){
        fprintf(stderr, "\nWrong CAN-frame format! Try:\n\n");
        fprintf(stderr, "    <can_id>#{R|data}          for CAN 2.0 frames\n");
        fprintf(stderr, "    <can_id>##<flags>{data}    for CAN FD frames\n\n");
        fprintf(stderr, "<can_id> can have 3 (SFF) or 8 (EFF) hex chars\n");
        fprintf(stderr, "{data} has 0..8 (0..64 CAN FD) ASCII hex-values (optionally");
        fprintf(stderr, " separated by '.')\n");
        fprintf(stderr, "<flags> a single ASCII Hex value (0 .. F) which defines");
        fprintf(stderr, " canfd_frame.flags\n\n");
        fprintf(stderr, "e.g. 5A1#11.2233.44556677.88 / 123#DEADBEEF / 5AA# / ");
        fprintf(stderr, "123##1 / 213##311\n     1F334455#1122334455667788 / 123#R ");
        fprintf(stderr, "for remote transmission request.\n\n");
        return 1;
    }

    /* open socket */
    if ((s = socket(PF_CAN, SOCK_RAW, CAN_RAW)) < 0) {
        perror("socket");
        return 1;
    }

    const char* ifrname = "can1";
    strcpy(ifr.ifr_name, ifrname);
    ifr.ifr_ifindex = if_nametoindex(ifr.ifr_name);
    if (!ifr.ifr_ifindex) {
        perror("if_nametoindex");
        return 1;
    }

    memset(&addr, 0, sizeof(addr));
    addr.can_family = AF_CAN;
    addr.can_ifindex = ifr.ifr_ifindex;
/*
    if (required_mtu > CAN_MTU) {

        //* check if the frame fits into the CAN netdevice 
        if (ioctl(s, SIOCGIFMTU, &ifr) < 0) {
            perror("SIOCGIFMTU");
            return 1;
        }
        mtu = ifr.ifr_mtu;

        if (mtu != CANFD_MTU) {
            printf("CAN interface is not CAN FD capable - sorry.\n");
            return 1;
        }

        //* interface is ok - try to switch the socket into CAN FD mode 
        if (setsockopt(s, SOL_CAN_RAW, CAN_RAW_FD_FRAMES,
                   &enable_canfd, sizeof(enable_canfd))){
            printf("error when enabling CAN FD support\n");
            return 1;
        }

        //* ensure discrete CAN FD length values 0..8, 12, 16, 20, 24, 32, 64 
        frame.len = can_dlc2len(can_len2dlc(frame.len));
    }
*/

    /* disable default receive filter on this RAW socket */
    /* This is obsolete as we do not read from the socket at all, but for */
    /* this reason we can remove the receive list in the Kernel to save a */
    /* little (really a very little!) CPU usage.                          */
    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);

    if (bind(s, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
        perror("bind");
        return 1;
    }

    /* send frame */
    printf("frame.len is %d\n", frame.len);
    printf("frame.can_id is %x\n", frame.can_id);
    if (write(s, &frame, required_mtu) != required_mtu) {
        perror("write");
        return 1;
    }

    close(s);

    return 0;
}

View Code

解析

1.message的格式；

    char* input = "008#abcd1234cdef567830";

其中‘008表示can_id，必须是三位十六进制数据，可以表示标准帧或者扩展帧；符号#“是can_id和can数据的分界符，最后的数据是报文的数据，标准帧一次最多只能发送8bits的数据，多余的数据自动丢弃；

2.parse_canframe函数，具体内容可参考lib.h和lib.c文件；

int parse_canframe(char *cs, struct canfd_frame *cf);
 /* parse CAN frame */
 required_mtu = parse_canframe(input, &frame);

function -- Transfers a valid ASCII string decribing a CAN frame into struct canfd_frame.

3.创建socket；

s = socket(PF_CAN, SOCK_RAW, CAN_RAW)

创建socket套接字

PF_CAN 为域位，同网络编程中的AF_INET，即ipv4协议；

SOCK_RAW使用的协议类型，SOCK_RAW表示原始套接字，报文头由自己创建；

CAN_RAW为使用的具体协议，为can总线协议；

4. 指定can口名称；

const char* ifrname = "can1";

5.设置过滤规则；发送数据则禁用过滤；

在数据接收时，系统可以根据预先设置的过滤规则，实现对报文的过滤。过滤规则使用can_filter结构体来实现，定义如下：

struct can_filter {  
canid_t can_id;  
canid_t can_mask;  
};

通过过滤规则可以在系统中过滤掉所有不符合规则的报文，使得应用程序不需要对无关的报文进行处理。在can_filter结构的can_id中，符号位CAN_INV_FILTER在置位时可以实现can_id在执行过滤前的位反转。用户可以为每个打开的套接字设置多条独立的过滤规则。

struct can_filter rfilter[2];  
rfilter[0].can_id   = 0x123;  
rfilter[0].can_mask = CAN_SFF_MASK;  // #define CAN_SFF_MASK 0x000007FFU  
rfilter[1].can_id   = 0x200;  
rfilter[1].can_mask = 0x700;  
setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));  // 设置规则

在极端情况下，如果应用程序不需要接收报文，可以禁用过滤规则。这样的话，原始套接字就会忽略所有接收到的报文。在这种仅仅发送数据的应用中，可以在内核中省略接收队列，以此减少CPU资源的消耗。

setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0); //Disable filter.

6.绑定socketCan；

bind(s, (struct sockaddr *)&addr, sizeof(addr)

bind函数用于绑定套接字，即将套接字和canbus外设进行绑定；

7.发送数据；

  /* send frame */  
    if (write(s, &frame, required_mtu) != required_mtu) {       //发送数据！  
        perror("write");  
        return 1;  
    }

8.数据格式的定义；

struct can_frame {
    canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
    __u8    can_dlc; /* frame payload length in byte (0 .. CAN_MAX_DLEN) */
    __u8    __pad;   /* padding */
    __u8    __res0;  /* reserved / padding */
    __u8    __res1;  /* reserved / padding */
    __u8    data[CAN_MAX_DLEN] __attribute__((aligned(8)));
};
struct canfd_frame {
    canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
    __u8    len;     /* frame payload length in byte */
    __u8    flags;   /* additional flags for CAN FD */
    __u8    __res0;  /* reserved / padding */
    __u8    __res1;  /* reserved / padding */
    __u8    data[CANFD_MAX_DLEN] __attribute__((aligned(8)));
};

#define CAN_MTU        (sizeof(struct can_frame))
#define CANFD_MTU    (sizeof(struct canfd_frame))