recovery code介绍

Recovery code是一种安全措施，用于帮助用户在忘记密码或丢失设备的情况下恢复其账户。当用户创建账户时，通常会被要求创建一个恢复代码。这个代码可以是一串数字、字母或符号组合，用户可以在需要时使用它来恢复他们的账户。如果用户忘记了他们的密码或者不再拥有他们的设备，他们可以使用恢复代码来验证他们的身份并重新获取对他们的账户的访问权限。因此，恢复代码是一种重要的安全措施，可以帮助用户保护其账户免受未经授权的访问。

相关问题

please show the code of fast retransmit of linux kernel

The fast retransmit algorithm in the Linux kernel TCP implementation can be found in the function `tcp_fastretrans_alert()` in the file `net/ipv4/tcp_input.c`:

static void tcp_fastretrans_alert(struct sock *sk, struct sk_buff *skb, int pkts_acked)
{
    struct tcp_sock *tp = tcp_sk(sk);
    struct tcp_sacktag_state sack_state;
    u32 prior_snd_una = tp->snd_una;
    int rexmit = 0;

    if (tp->frto <= tcp_jiffies32 &&
        !tcp_time_to_recover(sk, 0) &&
        !tp->tlp_high_seq &&
        tp->packets_out &&
        tcp_packets_in_flight(tp) <= tp->ssthresh &&
        !after(tp->snd_una, tp->high_seq)) {
        /* F-RTO RFC5682 */
        if (tcp_try_undo_recovery(sk)) {
            /* F-RTO undo recovery successful */
            tp->frto = 0;
            return;
        }
        /* F-RTO undo recovery unsuccessful */
        tcp_enter_frto(sk, skb);
        goto out;
    }
    ...
}

This function implements the Fast Retransmit algorithm, which is a mechanism used in TCP to detect packet loss and retransmit lost packets without waiting for a retransmission timeout. The algorithm works by detecting the receipt of three duplicate ACKs (i.e., three ACKs that acknowledge the same sequence number) and assuming that the missing packet is the one that was last transmitted before the three duplicates were received.

The `tcp_fastretrans_alert()` function checks whether the conditions for Fast Retransmit are met, and if so, it calls the `tcp_enter_frto()` function to initiate the retransmission. Otherwise, it continues with normal processing of the received ACK.

adc-keys0 { compatible = "adc-keys"; io-channels = <&saradc 0>; io-channel-names = "buttons"; poll-interval = <100>; keyup-threshold-microvolt = <1800000>; recovery-key { label = "F12"; linux,code = <KEY_F12>; press-threshold-microvolt = <0>; }; };每行代码解释

这是一个设备树中的节点定义，它描述了一个使用 SAR ADC（Successive Approximation Register ADC）读取按键状态的硬件设备。该节点的子节点定义了按键的详细信息，包括标签、Linux键值、阈值等等。

每行代码的解释如下：

adc-keys0 {

节点名称为 adc-keys0。

compatible = "adc-keys";

该节点描述的硬件设备类型是使用 ADC 读取按键状态的设备。

io-channels = <&saradc 0>;

IO通道绑定到 SAR ADC 的通道0。

io-channel-names = "buttons";

IO通道的名称为 "buttons"。

poll-interval = <100>;

设置轮询时间间隔为100个时间单位，具体时间单位取决于代码实现的上下文和使用场景。

keyup-threshold-microvolt = <1800000>;

KeyUp 阈值设置为1800000微伏。

recovery-key {

定义一个名为 recovery-key 的子节点。

label = "F12";

设置按键的标签为 "F12"。

linux,code = <KEY_F12>;

设置 Linux 中使用的键码为 KEY_F12。

press-threshold-microvolt = <0>;

Press 阈值设置为0。