Ch4 Internal Representation of Files高级操作系统课件PPT(UNIX).pptVIP

85%的文件小于8K，48％的文件小于1K 2。Inode节点占据1个块，存inode和文件内容，如果存不下，就存文件尾 4.2 Structure of a Regular File Two extension to the inode structure: Larger logical disk block More data the kernel can access on the disk in a single operation, the faster file access become Store file data in the inode Expanding the inode to occupy an entire disk block 4.3 Directories A directory is a file Its data is a sequence of entries: an inode number (2 bytes) the name of a file contained in the directory(14bytes) Every directory contains the file names dot and dot-dot(“.” and “..”) The inode numbers are those of the directory and its parent directory 4.3 Directories 4.3 Directories The kernel stores data for a directory just as it stores data for an ordinary file Processes may read directories in the same way they read regular file The kernel reserves exclusive right to write a directory The access permissions of a directory: Read: allows a process to read a directory Write: allows a process to create new directory entries / remove old one( creat, mknod, link, unlink ) Execute: search the directory for a file name 4.4 Conversion of a Path Name to an Inode The process access to a file by its path name The kernel works internally with inode rather than with path names The kernel converts the path name to inode 4.4 Conversion of a Path Name to an Inode Every process is associated with a current directory The u area contains a pointer to the current directory inode The current directory of the first process( process 0), is the root directory The current directory of every other starts out as the current directory of its parent process at the time it was created 4.4 Conversion of a Path Name to an Inode namei Working inode: namei use intermediate inodes as it parses a path name The inode where the search starts is the first working inode. Make sure the working inode is a directory The process must have permission to search the dir The userID of the process must match the owner or group ID of