下面有2个示例：
     1：保存机器从开机到结束的VBATT；
    2：保存uart接收到的数据到文件；

意义不多说了。

以下是代码：

#include <linux/fs.h>
#include <asm/uaccess.h>
#include <asm/unaligned.h>

static  struct file *fp =NULL;

int  write_to_file (char *buf, int size)
{
     int ret = 0;
     struct file *fp;
     mm_segment_t old_fs;
     loff_t pos = 0;
     int nwrite = 0;
     static int offset = 0;
     static int first_flag=0;

     /* change to KERNEL_DS address limit */
     old_fs = get_fs();
     set_fs(KERNEL_DS);


     if( first_flag==0){
     first_flag=1;
     /* open file to write */
     fp = filp_open("/data/at_log1", O_WRONLY|O_CREAT, 0640);
     if (!fp) {
         printk("%s: open file error\n", __FUNCTION__);
         ret = -1;
         goto exit;
         }
     }
     pos=(unsigned long)offset;

     /* Write buf to file */
     nwrite=vfs_write(fp, buf, size, &pos);
     offset +=nwrite;

exit:

     return ret;
}



int xxxx_exit(void){
if (fp)
          filp_close(fp, NULL);
}

1:保存VBATT与SOC：

static int adjust_soc(struct pm8921_bms_chip *chip, int soc,
        int batt_temp, int chargecycles,
        int rbatt, int fcc_uah, int uuc_uah, int cc_uah)
{
    ------------
   static char vbatt[100];
    rc = pm8921_bms_get_simultaneous_battery_voltage_and_current(
                            &ibat_ua,
                            &vbat_uv);
    if (rc < 0) {
        pr_err("simultaneous vbat ibat failed err = %d\n", rc);
        goto out;
    }

    chip->vbat_mv= vbat_uv/1000;
    sprintf(vbatt,"%d        %d\n",the_chip->vbat_mv,calculated_soc);
    write_to_file(vbatt,strlen(vbatt));
    ----------
}

2：将串口接收到的字符转化为16进制保存到文件中：

static void msm_serial_hs_rx_tlet(unsigned long tlet_ptr)
{
  
    ---------------
    static char temp[1024];

    rx_count = msm_hs_read(uport, UARTDM_RX_TOTAL_SNAP_ADDR);

    /* order the read of rx.buffer */
    rmb();

    if (0 != (uport->read_status_mask & CREAD)) {
        retval = tty_insert_flip_string(tty, msm_uport->rx.buffer,
                        rx_count);
        if (retval != rx_count) {
            msm_uport->rx.buffer_pending |= CHARS_NORMAL |
                retval << 5 | (rx_count - retval) << 16;
        }
        if(rx_count<=512){
            //memcpy(temp,msm_uport->rx.buffer,rx_count);
            for(i=0;i<rx_count;i++){
            sprintf(temp+2*i,"%02x",msm_uport->rx.buffer[i]);
            write_to_file(temp,strlen(temp));
            }
                
        }
          ----------------
}