dentry

In the previous blog, the four data structures in the General Virtual File model provided by the kernel are extremely operational. How are these objects connected in order to make various file systems get along in harmony. This blog will focus on how they interact with the kernel, including how they interact with processes and some related caching mechanisms. 1. process-related files First, the file must be opened by the process. Each process has its own working directory and its own root direc

, whenreadWhen a function reads a file, the data is returned normally. Although most file system code is in the kernel, 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. 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

;s_dev = 0;s->s_bdev = 0;s->s_type = Null;unlock_super (s); return NULL;} static struct Super_block *devfs_read_super (struct super_block *sb, void *data, int silent) {struct Inode *root_in Ode = NULL; if (get_root_entry () = = NULL) goto out_no_root; Atomic_set (fs_info.devfsd_overrun_count, 0); Init_waitqueue_head (fs_info.devfsd_wait_queue); Init_waitqueue_head (fs_info.revalidate_wait_queue); FS_INFO.SB = SB; SB-GT;U.GENERIC_SBP = fs_info; Sb->s_blocksize = 1024; S

ricard, that is, the information corresponding to the home directory. 　　 Of course, if an error is found during the search process, for example, the parent directory of the directory to be created does not exist, or the current process does not have the corresponding permissions, the system will call the relevant process for processing in this case, in this case, I will not mention it. 　　 In Linux, sys_mkdir is called by the system to add new nodes to the VFS directory tree. In addition, the fo

Article title: linux file system issues. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source. Question 1: How does the kernel handle a specific file? Answer: (1) search in the directory item cache. Note that the query is performed through the Hasse function, and the query order is from right to left. E.g. Processing/usr/src/jiawei. c will start from jiawei. c and

, see the following section .)[7] Call d_make_root () to create and initialize a directory for the root inode. ------------------------------------------------------Purpose: search for or create a VFS super_block structure. Execute ramfs_fill_supper () to overwrite ramfsBlock. Then, add one to the reference count of the root directory.Struct dentry * ramfs_mount (struct file_system_type * fs_type,Int flags, const char * dev_name, void * data ); ------

imagine, tracking installed file systems will soon become a nightmare. For each installation operation, the kernel must store the installation points and installation marks in the memory, and the relationship between the file system to be installed and other installed file systems. Therefore, we need a data structure that retains the installation information to clarify these relationships. Such information is stored in the installed file system descriptor. Each descriptor is a data structure wi

The following error was found during the installation of Vmtools on the CentOS virtual machine /tmp/modconfig-ygOywn/vmhgfs-only/inode.c: 在函数‘HgfsPermission’中: tmp/modconfig-ygOywn/vmhgfs-only/./shared/compat_dcache.h:57:38: 错误：‘struct dentry’没有名为‘d_count’的成员 #define compat_d_count(dentry) dentry->d_count ^ /tmp/modconfig-ygOywn/vmhgfs-only/inode.c:1904:23: 附注：in

root, from detaching the file system. You can also prohibit anyone from attaching a file system to the current file system to overwrite it. 2.2 how does LIDS protect files in the kernel? In this section, we will see some kernel code to understand how LIDS protects files. Linux File System Data Structure Program First, we must understand the Virtual File System of linux. Every file in linux has a node inode no matter what it looks like. The file system provides the following data structure. In/u

not be successfully implemented.In fact, after the installation is complete, regardless of successful failure can be viewed through vmware-config-tools.pl. Once again, I see the following information:/TMP/MODCONFIG-YGOYWN/VMHGFS-ONLY/INODE.C: In function ' hgfspermission ':/tmp/modconfig-ygoywn/vmhgfs-only/./shared/ COMPAT_DCACHE.H:57:38: Error: ' struct dentry ' does not have a member named ' D_count ' #define COMPAT_D_COUNT (

Article Title: Counting mechanism for metadata in Linux File Systems. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source. In Linux File Systems, the reference count of metadata is mainly used to manage the creation, use, and release of metadata (such as inode and dentry structures) in memory. Understanding this mechani

; ----> device number. Umode_t I _mode; Nlink_t I _nlink; Uid_t I _uid; ...... } Note: it is used to identify a node inode. This means that you can use a pair to obtain the unique inode in a system. In/ur/src/linux/cinclude/linux/dcache. h Struct dentry { Int d_count; Unsigned int d_flags; Struct inode * d_inode;/* Where the name belongs to-NULL is negative */ Struct dentry * d_parent;/* parent directory */

files, symbolic connection files and so on) information, which means that the operating system can traverse the directory to determine the symbolic connection, Since you can determine the symbolic connection of course, you can take some measures to prevent entering a large cycle, the system in the continuous encounter 8 symbols connected to stop the traversal, which is why the directory symbol connection will not enter the cause of the dead loop.　　But for the hard connection, because of the dat

Virtual file system, an alias virtual file system switch, is a software layer in Linux that provides a file system operation interface to user space.The system calls that the VFS contains include open (2), stat (2), read (2), write (2), chmod (2), and so on, which are executed in the process environment. The following important data structures are the VFS (the data structures involved in the virtual file system): 1. Directory Entry Cache (dcache)The VFS implements system calls to open (2), stat

files, etc.) information, that is, the operating system in the traversal directory can be judged by the symbolic connection, Since it is possible to determine the symbolic connection can certainly take some measures to prevent the entry into the excessive cycle, the system in a row after the 8 symbolic connection stop traversal, which is why the directory symbol connection will not enter the dead loop reason. However, for hard connection, due to the data structure and algorithm limitations adop

shown in figure: kernelhacking---> [*]debug filesystem Drivers need to include header file Use the following command: Mount-t Debugfs none/mnt Then you can see the files we created in the system after entering the/mnt. Let's start by saying how to use Debugfs in a driver. First we need to create a directory of our own, using the following functions: struct Dentry *debugfs_create_dir (const char *name, struct

Linux-26 file opening process involves data structure analysis: http: blogcsdnnetordeder Linux-2.6 file opening process involves data structure analysis: Link: http://blog.csdn.net/ordeder/article/details/24420637User level The file is opened in the following structure: Fd = open (path, flag, mode)Kernel layer After the open function is trapped in the kernel space, perform the following operations: The system traverses the path based on the path. In linux, everything is a file, including direct

= compat_sock_ioctl,#endif.mmap =sock_mmap,.open =sock_no_open,/* special open code to disallow open via /proc */.release =sock_close,.fasync =sock_fasync,.sendpage =sock_sendpage,.splice_write = generic_splice_sendpage,.splice_read =sock_splice_read,}; Bind the set interface file to the set Interface The Application Layer accesses the set interface through the file descriptor. Therefore, when the socket system is called to create the set interface, sock_map_fd () is called after creation

);Out:Return err_ptr (error );} Then, the do_new_mount () function calls do_add_mount ():Int do_add_mount (struct vfsmount * newmnt, struct nameidata * nd,Int mnt_flags, struct list_head * fslist){Int err; Down_write ( namespace_sem );/* Something was mounted here while we slept */While (d_mountpoint (Nd-> dentry) follow_down ( Nd-> MNT, Nd-> dentry ));Err =-einval;If (! Check_mnt (Nd-> MNT ))Goto unlock