how to access file in kernel space

本文介绍了一个静态函数write_file,该函数用于将指定的数据写入到Linux系统中的文件。通过设置内存段、打开文件、写入数据并进行错误处理等步骤实现。文中详细展示了使用系统调用进行文件操作的过程。

摘要生成于 C知道 ,由 DeepSeek-R1 满血版支持, 前往体验 >

static void write_file(char *filename,  unsigned char *data, unsigned int nSize)
{
      struct file *file;
      loff_t pos = 0;
      int fd;

      dmac_inv_range(data, data + nSize);

      mm_segment_t old_fs = get_fs();
      set_fs(KERNEL_DS);
      fd = sys_open(filename, O_WRONLY|O_CREAT, 0644);
      if (fd >= 0) {
           sys_write(fd, data, nSize);
           file = fget(fd);
           if (file) {
                       vfs_write(file, data, nSize, &pos);
                       fput(file);
           }
           sys_close(fd);
       }
       else
      {
           mfc_err("........Open fail : %d \n", fd);
       }
       set_fs(old_fs);

       dmac_clean_range(data, data + nSize);

}
### DWC3 Endpoint Configuration and Usage in USB Driver Development In USB driver development, configuring endpoints (EPs) is crucial for establishing communication between a device and host. For the DesignWare Core USB 3.0 (DWC_usb3 or DWC3), each endpoint has specific attributes that must be set up correctly to ensure proper data transfer. Endpoints within DWC3 are bidirectional entities but operate unidirectionally at any given time; they can either send or receive data depending on their direction setting[^1]. When initializing an endpoint, several parameters need attention: - **Direction**: Determines whether EP will act as IN (device-to-host) or OUT (host-to-device). - **Type**: Specifies if it’s Control, Isochronous, Bulk, or Interrupt. - **Maximum Packet Size (MPS)**: Defines maximum size of packets this EP handles during transfers. For configuration purposes, developers often interact with structures like `struct dwc3_ep` which encapsulates all necessary details about an individual endpoint including its capabilities and current state. This structure also contains pointers to DMA buffers used by hardware when performing actual I/O operations. To manage these configurations programmatically, one typically uses functions provided by the DWC3 core layer such as `dwc3_endpoint_config()` where appropriate settings from user space get applied directly into corresponding registers via register access methods implemented inside drivers/usb/dwc3/core.c file[^2]. Additionally, managing queues associated with endpoints involves using linked lists similar to those found while working with other types of devices utilizing generic Linux kernel APIs. Specifically, `struct list_head` plays a significant role here allowing efficient addition/removal of requests without disrupting ongoing transactions significantly impacting performance positively especially under heavy load conditions. ```c // Example C code snippet showing how to configure an endpoint void example_configure_dwc3_endpoint(struct dwc3 *dwc3, struct dwc3_ep *dep) { u8 ep_type; /* Set endpoint type */ dep->endpoint.type = ep_type; /* Configure Maximum Packet Size based on requirements */ dwc3_set_maximum_packet_size(dwc3, dep); /* Apply changes through low-level interface */ dwc3_gadget_writel(dwc3, DGCMD_SET_CONFIG_EP, &config); } ``` --related questions-- 1. How does the DWC3 handle different types of USB transfers? 2. What mechanisms exist for error handling in DWC3 endpoint communications? 3. Can you explain more about the role of DMA buffers in DWC3 operation? 4. In what scenarios would adjusting the MPS value impact system performance?
评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值