dentry

discussed later ), however, the architecture shown in Figure 1 shows the relationship between the user space and the main components related to the file system in the kernel. Figure 1. Architecture of Linux File System Components The user space contains applications (such as file system users) and the gnu c library (glibc), which provide user interfaces for file system calls (open, read, write, and close. The function of a system call interface is like a switch, which sends system calls fro

maintains the concept of a disk inode, which represents an actual file. At the previous layer, Linux maintains the memory inode, it allows the operating system to provide user interfaces to operate disk inode. The memory inode corresponds to the disk inode, in the VFS layer, disk inode in different formats of different file systems are unified into the same memory inode. In this way, the interfaces provided above are unified. Before the interfaces are unified, the data structure must be unified

0.sys_open () (1) Find an idle item from the Open File table of the current process get_unused_fs () (2) Establish the context Filp_open () of file read and write (see 1) (3) Install the context in the File open table 1.filp_open (): Creating a context for file reading and writing (1) Get the Dentry and Vfsmount:open_namei () pointing to the filename. If only open, search by Path_init () and Path_walk () If there is a requirement to create, t

After the kernel unlocks rootfs. initramfs, VFS builds a tree in the kernel. We write a simple code to traverse the tree: Static void vfswalk (cvfswalk * pwalk, void * pparent, dentry * pentry) { // Insert all child nodes Struct dentry * pnode; Void * plast = NULL; List_for_each_entry (struct dentry, pnode, pentry-> d_subdirs, d_u.d_child) { Plast = pwalk-> inse

, convert to Dentry(Error = do_last (nd, File, op, opened)) > 0) {The last step of//open, finding the inode by Dentry, and finally calling Vfs_openNd->flags = ~ (lookup_open| lookup_create| LOOKUP_EXCL);s = trailing_symlink (nd);if (Is_err (s)) {Error = Ptr_err (s);Break}}Terminate_walk (ND);Out2:if (! ( Opened file_opened)) {BUG_ON (!error);PUT_FILP (file);}if (unlikely (error)) {if (Error = =-eopenstale)

storage block on the storage device is maintained by the operating system.The Linux file system interface is implemented as a layered architecture that separates the user interface layer, the file system implementation, and the driver that operates the storage device.VFS is the primary interface for the underlying file system. This component exports a set of interfaces and then abstracts them into individual file systems, and the behavior of individual file systems can vary greatly. There are t

Figure 1. Architecture of Linux File system componentsThe user space contains applications (for example, the users of the file system) and the GNU C Library (GLIBC), which provide a user interface for file system calls (open, read, write, and close). The system invocation interface acts like a switch that sends system calls from the user space to the appropriate endpoints in the kernel space.VFS is the primary interface for the underlying file system. This component exports a set of interfaces a

, c_fops); Note: In the code, C_open does not actually have any use, because C_read and c_write directly refer to the global variable hello. Here, we can also change the wording, in the Read/write function with Filp->private_data to refer to the character array hello.Here, three files and subdirectories have been created. In Module_exit, we have to remember to release the created data. 1 debugfs_remove_recursive(my_debugfs_root); Debugfs_remove_recursive c

passed to any function that operates on the file. After all instances in the file are closed, the kernel releases the data structure. In kernel creation and driver source code, struct file pointers are usually named file or filp. As follows:Struct file {Union {Struct list_head fu_list; file object linked list pointer Linux/include/Linux/list. hStruct rcu_head fu_rcuhead; RCU (read-copy update) is a new lock mechanism in Linux 2.6 kernel.} F_u;Struct path f_path; contains

requests.file_operationsStructreleaseThe Member is used to complete the user programcloseThe request is calledreleaseInsteadcloseIt does not necessarily close the file, but reduces the reference count. Only when the reference count is reduced to 0 will the file be closed. For general files opened on the same file system,read,writeThe file operation steps and methods should be the same, and the called functions should be the same, so the three open files in the figurefileThe struct points to the