Linux SocketCAN中canfd_帧中的“flags”字段是什么？

非FD（“传统”）CAN帧在SocketCAN中具有以下格式：

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

帧ID、长度和数据都有清晰的位置，加上一些我们不担心的填充。不过，对于CAN-FD帧，还有一个额外字段：

struct canfd_frame {
        canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
        __u8    len;     /* frame payload length in byte (0 .. 64) */
        __u8    flags;   /* additional flags for CAN FD */
        __u8    __res0;  /* reserved / padding */
        __u8    __res1;  /* reserved / padding */
        __u8    data[64] __attribute__((aligned(8)));
};

flags

字段看起来很有用，但我没有找到关于它实际包含的内容的文档。它是内部的（即由内核设置的）？可能的标志是什么，它们是什么意思

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谢谢大家!

我在这里找到了一些信息：

如果我理解正确，ESI位仅适用于虚拟CAN接口上的测试。不过，BRS位的级别相当低，这并没有指定硬件是自动设置还是取消设置

/*
 * defined bits for canfd_frame.flags
 *
 * The use of struct canfd_frame implies the Extended Data Length (EDL) bit to
 * be set in the CAN frame bitstream on the wire. The EDL bit switch turns
 * the CAN controllers bitstream processor into the CAN FD mode which creates
 * two new options within the CAN FD frame specification:
 *
 * Bit Rate Switch - to indicate a second bitrate is/was used for the payload
 * Error State Indicator - represents the error state of the transmitting node
 *
 * As the CANFD_ESI bit is internally generated by the transmitting CAN
 * controller only the CANFD_BRS bit is relevant for real CAN controllers when
 * building a CAN FD frame for transmission. Setting the CANFD_ESI bit can make
 * sense for virtual CAN interfaces to test applications with echoed frames.
 */