echo＆＃34;次要号码＆＃34; ＆GT; misc char驱动程序 - 被截断

Question

我已经编写了一个misc char驱动程序，当我将驱动程序的次要编号回显到misc字符驱动程序时，它没有收到第一个数字。

写函数是这样的，

static ssize_t hellowld_write(struct file *file, const char *buf,size_t len, 
                loff_t *ppos)
{
    pr_debug("In hellowld_write len %d buf %s \n",len,buf);
    minor[0] = '\0';    
    snprintf(minor, 20,"%d", hellowld_device.minor);
    strncpy(inputminor, buf,len);
    pr_debug("In hellowld_write -- minor %s -- recvNum  %s end\n",minor, inputminor);
    pr_debug("In hellowld_write -- strlen minor %d -- strlen inputminor  %d end\n", strlen(minor), strlen(inputminor));
    if( strncmp(minor, inputminor, strlen(minor)) ==  0)
    {
        pr_debug("In hellowld_write -- strcmp passed \n");
        return strlen(minor);   
    }
    else 
    {
        pr_debug("In hellowld_write -- strcmp failed \n");
        return -EFAULT;
    }   
}

当我这样做的时候 回声＆＃34; 54＆＃34; ＆GT;的/ dev / HELLOWLD

Dec 31 11:36:40 pavan-linux kernel: [16981.382424] In hellowld_write len 1 buf 
Dec 31 11:36:40 pavan-linux kernel: [16981.382424] 
Dec 31 11:36:40 pavan-linux kernel: [16981.382424] o
Dec 31 11:36:40 pavan-linux kernel: [16981.382437] In hellowld_write -- minor 54 -- recvNum  
Dec 31 11:36:40 pavan-linux kernel: [16981.382437] 4
Dec 31 11:36:40 pavan-linux kernel: [16981.382437]  end
Dec 31 11:36:40 pavan-linux kernel: [16981.382444] In hellowld_write -- strlen minor 2 -- strlen inputminor  3 end
Dec 31 11:36:40 pavan-linux kernel: [16981.382448] In hellowld_write -- strcmp failed 

回声＆＃34; 22＆＃34; ＆GT;的/ dev / HELLOWLD

Dec 31 11:36:52 pavan-linux kernel: [16993.356993] In hellowld_write len 3 buf 22
Dec 31 11:36:52 pavan-linux kernel: [16993.356993] 
Dec 31 11:36:52 pavan-linux kernel: [16993.356993] o
Dec 31 11:36:52 pavan-linux kernel: [16993.357011] In hellowld_write -- minor 54 -- recvNum  22
Dec 31 11:36:52 pavan-linux kernel: [16993.357011]  end
Dec 31 11:36:52 pavan-linux kernel: [16993.357017] In hellowld_write -- strlen minor 2 -- strlen inputminor  3 end
Dec 31 11:36:52 pavan-linux kernel: [16993.357021] In hellowld_write -- strcmp failed 

为什么当我回显次要号码时，hellowld_write中收到的数据会被截断？