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File driver6/29/2023 ![]() If you want to know exactly what are the general information about the file, you should explore the member elements of the inode. That holds general information about a file. So, an inode is a VFS data structure the data structure is struct inode. Unix makes a clear distinction between the contents of a file and the information about the file. Let’s explore about this inode object and this file object. Apart from these two, these two are another two important data structures a which are involved during file access, whether it could be a normal file or a device file. Cdev has a field, which holds the pointer to this a file operation variable what we created in the driver file. While registering the cdev, we initialize the cdev’s file operation with our drivers file operation methods.īasically, cdev points to Struct file_ops. You may be a familiar with this, struct cdev? which represents a character device, and we registered this struct cdev using cdev_add. The important data structures involved are struct inode, struct cdev, struct file operations, and struct file. Let’s explore more about a struct inode and struct file.ĭuring file operation of a regular file or a device file, there are various VFS data structures involved. And the second argument what it passes is a pointer of file object. The first argument is pointer of Inode associated with file name, the device file name. When it calls the open method, it passes two arguments. The open system call execution is control is first passed to the VFS, and the VFS finds the appropriate driver, and it calls the open method of the driver. I’ll talk more on inode object and file object little later, but for a time being, you just have to remember this. When the VFS receives open request on a device file or on a regular file, what VFS does is it opens a file by creating a new file object and linking it to the corresponding inode object. This is a open method for the open system call, which is invoked on this device file. And from the VFS subsystem, the control is passed to the appropriate drivers open method. That is virtual file system.įrom user level, the control is first passed to the kernels VFS subsystem. The kernel will process that system call. You know the system is transferred to the kernel. When an open system call is used on this device file, what happens? And let’s say your driver has created a device file /dev/pcd let’s say the user process uses the open system call to open this device file. Let’s say you have loaded your pcd driver, ‘pcd’ stands for sudo character device driver. By using the struct file operation variable what you defined in your driver file.įirst, let’s explore the open method. So, you need to implement lseek, read, write, open, release methods in your driver, and after that, you have to initialize these member elements. In this article, we will be using lseek, read, write, open, and release. And all these are possible file operation methods for a regular file or for a device file. This structure is a collection of various functions pointers. This structure you can find in include/linux/fs.h. In the previous article, we created a variable of this struct type, struct file operations. In this character driver, we will give support to handle the below a user-level system calls as shown in Figure 1. And that what we are going to explore now, character driver file operation methods. The file operation variable a what we created is not yet initialized, so will initialize that later when we define our drivers file operation methods. In the previous article, we explored about the cdev_init() and cdev_add().We actually registered our character device using cdev, and the cdev structure is initialized with a file operation variable.
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