ext2文件系统源代码之namei.c

我们继续来看ext2文件系统源代码里的namei.c文件，这个文件的代码主要是文件名查找之类的操作函数，并不是很难。

/* * linux/fs/ext2/namei.c * * The only non-static object here is ext2_dir_inode_operations. * * 作者信息 * Copyright (C) 1992, 1993, 1994, 1995 * Remy Card ([e-mail]) * Laboratoire MASI - Institut Blaise Pascal * Universite Pierre et Marie Curie (Paris VI) * *  from * *  linux/fs/minix/namei.c * *  Copyright (C) 1991, 1992  Linus Torvalds * *  Big-endian to little-endian byte-swapping/bitmaps by *        David S. Miller ([e-mail]), 1995 */#include <linux/pagemap.h>#include "ext2.h"#include "xattr.h"#include "acl.h"#include "xip.h"/*增加目录和文件的连接*/static inline int ext2_add_nondir(struct dentry *dentry, struct inode *inode){/*ext2_add_link函数我们之前讲过，就是把dentry目录和inode文件建立连接*/int err = ext2_add_link(dentry, inode);/*如果建立连接成功，填充dentry的一些数据*/if (!err) {d_instantiate(dentry, inode);return 0;}/*建立连接失败，就减少inode的连接数目*/inode_dec_link_count(inode);iput(inode);return err;}/*在dir目录里查找dentry文件，dir是想要查找的文件所在目录的inode，dentry是想找的文件dentry，nd是辅助查找结构体，里边存放查找结果*/static struct dentry *ext2_lookup(struct inode * dir, struct dentry *dentry, struct nameidata *nd){struct inode * inode;ino_t ino;/*日常检查参数对不对，文件名字长度检查*/if (dentry->d_name.len > EXT2_NAME_LEN)return ERR_PTR(-ENAMETOOLONG);/*之前讲过的函数，在目录里根据文件名查找文件的inode，返回inode号码*/ino = ext2_inode_by_name(dir, dentry);inode = NULL;/*找到啦！*/if (ino) {/*从inode的ino编号得到文件的inode结构体*/inode = iget(dir->i_sb, ino);/*如果返回失败，返回权限错误*/if (!inode)return ERR_PTR(-EACCES);}/*把inode和dentry连接起来*/return d_splice_alias(inode, dentry);}/*获得dentry的父目录的dentry*/struct dentry *ext2_get_parent(struct dentry *child){unsigned long ino;struct dentry *parent;struct inode *inode;/*dotdot存放父目录的dentry结构体*/struct dentry dotdot;/*dotdot代表..*/dotdot.d_name.name = "..";dotdot.d_name.len = 2;/*使用我们之前讲过的ext2_inode_by_name函数，来得到父目录的inode号码*/ino = ext2_inode_by_name(child->d_inode, &dotdot);if (!ino)return ERR_PTR(-ENOENT);/*根据号码得到inode结构体*/inode = iget(child->d_inode->i_sb, ino);/*获取失败，返回权限错误*/if (!inode)return ERR_PTR(-EACCES);/*调用dcache的d_alloc_anon函数，分配一个dentry结构体*/parent = d_alloc_anon(inode);/*失败返回没有内存*/if (!parent) {iput(inode);parent = ERR_PTR(-ENOMEM);}/*分配成功，返回父目录的dentry结构体*/return parent;} /* ext2的创建新文件，在创建这个文件之前，我们已经创建好了dentry结构体，但是没有inode结构体 */static int ext2_create (struct inode * dir, struct dentry * dentry, int mode, struct nameidata *nd){/*创建inode结构体*/struct inode * inode = ext2_new_inode (dir, mode);int err = PTR_ERR(inode);/*inode正确的话*/if (!IS_ERR(inode)) {/*inode的inode操作函数集合指向ext2_file_inode_operations*/inode->i_op = &ext2_file_inode_operations;/*ext2是使用片内执行的硬件，地址空间函数操作和文件操作函数不一样*/if (ext2_use_xip(inode->i_sb)) {inode->i_mapping->a_ops = &ext2_aops_xip;inode->i_fop = &ext2_xip_file_operations;} else if (test_opt(inode->i_sb, NOBH)) {/*没有缓冲区的inode，使用另一套地址空间操作函数和文件操作函数*/inode->i_mapping->a_ops = &ext2_nobh_aops;inode->i_fop = &ext2_file_operations;} else {/*使用一般的函数集合*/inode->i_mapping->a_ops = &ext2_aops;inode->i_fop = &ext2_file_operations;}/*修改过，就标记inode脏*/mark_inode_dirty(inode);/*建立dentry和inode的连接*/err = ext2_add_nondir(dentry, inode);}return err;}/*ext2根据文件模式和设备号新建一个inode*/static int ext2_mknod (struct inode * dir, struct dentry *dentry, int mode, dev_t rdev){struct inode * inode;int err;/*判断设备号是不是合法*/if (!new_valid_dev(rdev))return -EINVAL;/*新建inode结构体*/inode = ext2_new_inode (dir, mode);err = PTR_ERR(inode);if (!IS_ERR(inode)) {/*特殊设备的inode初始化，根据文件的类型不同设置不同的操作函数集合*/init_special_inode(inode, inode->i_mode, rdev);/*配置了文件属性才会有*/#ifdef CONFIG_EXT2_FS_XATTR/*特殊文件的操作结构体集合*/inode->i_op = &ext2_special_inode_operations;#endif/*写后都要标记脏*/mark_inode_dirty(inode);/*建立目录和inode的连接*/err = ext2_add_nondir(dentry, inode);}return err;}/*ext2建立软链接，dir是要建立的连接所在的目录，dentry是链接文件的dentry，symname是软连接文件爱你明*/static int ext2_symlink (struct inode * dir, struct dentry * dentry,const char * symname){/*获得vfs层的超级块结构体*/struct super_block * sb = dir->i_sb;int err = -ENAMETOOLONG;/*l存放连接名字长度*/unsigned l = strlen(symname)+1;struct inode * inode;/*看看连接名字是不是太长*/if (l > sb->s_blocksize)goto out;/*新建一个软链接文件，user，group和other都对他有读写执行权限*/inode = ext2_new_inode (dir, S_IFLNK | S_IRWXUGO);err = PTR_ERR(inode);if (IS_ERR(inode))goto out;/*ext2文件系统里，ext2_inode_info结构体的i_data用来存放软链接的文件名，这叫做快速链接，如果放不下就放在块里，这叫做慢速链接*/if (l > sizeof (EXT2_I(inode)->i_data)) {/*慢连接的inode操作函数*/inode->i_op = &ext2_symlink_inode_operations;/*无缓冲区和有缓冲区的地址空间操作函数*/if (test_opt(inode->i_sb, NOBH))inode->i_mapping->a_ops = &ext2_nobh_aops;elseinode->i_mapping->a_ops = &ext2_aops;/*fs层的软链接与页的链接*/err = page_symlink(inode, symname, l);if (err)goto out_fail;} else {/* 快速链接的inode函数操作集合设置 */inode->i_op = &ext2_fast_symlink_inode_operations;/*把链接的名字放在i_data里*/memcpy((char*)(EXT2_I(inode)->i_data),symname,l);/*i_size是文件大小，就是软链接名字长度*/inode->i_size = l-1;}/*写过以后标记为脏*/mark_inode_dirty(inode);/*建立目录和软链接的连接*/err = ext2_add_nondir(dentry, inode);out:return err;out_fail:/*失败后就会减少软链接的引用计数*/inode_dec_link_count(inode);iput (inode);goto out;}/*建立目录的inode和dentry之间的硬连接，因为是硬连接，所以其实上是有两个dentr指向inode*/static int ext2_link (struct dentry * old_dentry, struct inode * dir,struct dentry *dentry){/*获得原先的dentry的inode*/struct inode *inode = old_dentry->d_inode;/*如果已经超过了最大限制，返回错误*/if (inode->i_nlink >= EXT2_LINK_MAX)return -EMLINK;/*修改时间*/inode->i_ctime = CURRENT_TIME_SEC;/*增加inode的链接计数*/inode_inc_link_count(inode);atomic_inc(&inode->i_count);/*把新的dentry也指向inode*/return ext2_add_nondir(dentry, inode);}/*新建一个目录，dir是新建的目录在的父目录，新建的额目录的dentry*/static int ext2_mkdir(struct inode * dir, struct dentry * dentry, int mode){struct inode * inode;int err = -EMLINK;/*子目录过多了*/if (dir->i_nlink >= EXT2_LINK_MAX)goto out;/*增加dir的计数*/inode_inc_link_count(dir);/*新建一个目录的inode*/inode = ext2_new_inode (dir, S_IFDIR | mode);err = PTR_ERR(inode);if (IS_ERR(inode))goto out_dir;/*为新建的目录inode设置操作函数*/inode->i_op = &ext2_dir_inode_operations;inode->i_fop = &ext2_dir_operations;/*地址空间操作函数集合*/if (test_opt(inode->i_sb, NOBH))inode->i_mapping->a_ops = &ext2_nobh_aops;elseinode->i_mapping->a_ops = &ext2_aops;/*目录的inode增加引用计数*/inode_inc_link_count(inode);/*新建的目录，肯定是空的，清空*/err = ext2_make_empty(inode, dir);if (err)goto out_fail;/*建立dentry和inode的链接*/err = ext2_add_link(dentry, inode);if (err)goto out_fail;/*用inode的一些数据填充dentry*/d_instantiate(dentry, inode);out:return err;out_fail:inode_dec_link_count(inode);inode_dec_link_count(inode);iput(inode);out_dir:inode_dec_link_count(dir);goto out;}/*释放目录对于目录项的链接*/static int ext2_unlink(struct inode * dir, struct dentry *dentry){/*目录项的inode*/struct inode * inode = dentry->d_inode;struct ext2_dir_entry_2 * de;struct page * page;int err = -ENOENT;/*在dir目录里寻找dentry目录项*/de = ext2_find_entry (dir, dentry, &page);if (!de)goto out;/*在目录项列表里删除这个目录项*/err = ext2_delete_entry (de, page);if (err)goto out;/*修改时间和减少这个被删除目录项的引用计数*/inode->i_ctime = dir->i_ctime;inode_dec_link_count(inode);err = 0;out:return err;}/*删除目录，dir是删除的目录的父目录，dentry是删除的目录的dentry*/static int ext2_rmdir (struct inode * dir, struct dentry *dentry){/*要删除目录的inode*/struct inode * inode = dentry->d_inode;int err = -ENOTEMPTY;/*把要删除的目录清空*/if (ext2_empty_dir(inode)) {/*然后解除父目录对于子目录的链接*/err = ext2_unlink(dir, dentry);if (!err) {/*把子目录文件大小置为0，减少引用计数*/inode->i_size = 0;inode_dec_link_count(inode);inode_dec_link_count(dir);}}return err;}/*重命名目录名字，old_dir是老的目录的父目录inode，old_dentry是老的目录的目录项结构体，new_dir是新的目录的父目录，new_dentry是新的目录项*/static int ext2_rename (struct inode * old_dir, struct dentry * old_dentry,struct inode * new_dir,struct dentry * new_dentry ){/*新老目录的inode*/struct inode * old_inode = old_dentry->d_inode;struct inode * new_inode = new_dentry->d_inode;struct page * dir_page = NULL;struct ext2_dir_entry_2 * dir_de = NULL;struct page * old_page;struct ext2_dir_entry_2 * old_de;int err = -ENOENT;/*在老的目录里寻找老的目录项*/old_de = ext2_find_entry (old_dir, old_dentry, &old_page);if (!old_de)goto out;/*如果这个文件是一个目录的话，就先获得这个目录的父目录项*/if (S_ISDIR(old_inode->i_mode)) {err = -EIO;/*得到这个目录项的父目录*/dir_de = ext2_dotdot(old_inode, &dir_page);if (!dir_de)goto out_old;}/*如果这个新的目录项有inode*/if (new_inode) {struct page *new_page;struct ext2_dir_entry_2 *new_de;err = -ENOTEMPTY;/*清空这新建的目录，如果没有成功，跳转到out_dir*/if (dir_de && !ext2_empty_dir (new_inode))goto out_dir;err = -ENOENT;/*在新目录里寻找新的目录项*/new_de = ext2_find_entry (new_dir, new_dentry, &new_page);if (!new_de)goto out_dir;/*增加原先的目录项的引用计数*/inode_inc_link_count(old_inode);/*设置新目录对新目录项的链接*/ext2_set_link(new_dir, new_de, new_page, old_inode);/*修改时间*/new_inode->i_ctime = CURRENT_TIME_SEC;/*释放原先的连接*/if (dir_de)drop_nlink(new_inode);/*增加新的目录项引用计数*/inode_dec_link_count(new_inode);} else {/*新的目录项还没有inode，说明是一个硬连接*/if (dir_de) {err = -EMLINK;if (new_dir->i_nlink >= EXT2_LINK_MAX)goto out_dir;}/*硬连接增加inode引用计数*/inode_inc_link_count(old_inode);/*建立新目录项和原先的inode连接*/err = ext2_add_link(new_dentry, old_inode);if (err) {inode_dec_link_count(old_inode);goto out_dir;}if (dir_de)inode_inc_link_count(new_dir);}/*修改时间*/old_inode->i_ctime = CURRENT_TIME_SEC;/*在老的目录上删除老的目录项*/ext2_delete_entry (old_de, old_page);/*减少其引用计数*/inode_dec_link_count(old_inode);/**/if (dir_de) {/*把原先目录和新的文件连接起来*/ext2_set_link(old_inode, dir_de, dir_page, new_dir);/*减少原先的目录连接计数*/inode_dec_link_count(old_dir);}return 0;out_dir:/*操作失败，释放原先的目录结构体*/if (dir_de) {kunmap(dir_page);page_cache_release(dir_page);}out_old:kunmap(old_page);page_cache_release(old_page);out:return err;}/*目录的inode操作函数映射表*/const struct inode_operations ext2_dir_inode_operations = {.create= ext2_create,.lookup= ext2_lookup,.link= ext2_link,.unlink= ext2_unlink,.symlink= ext2_symlink,.mkdir= ext2_mkdir,.rmdir= ext2_rmdir,.mknod= ext2_mknod,.rename= ext2_rename,#ifdef CONFIG_EXT2_FS_XATTR.setxattr= generic_setxattr,.getxattr= generic_getxattr,.listxattr= ext2_listxattr,.removexattr= generic_removexattr,#endif.setattr= ext2_setattr,.permission= ext2_permission,};/*特殊文件的inode操作函数表*/const struct inode_operations ext2_special_inode_operations = {#ifdef CONFIG_EXT2_FS_XATTR.setxattr= generic_setxattr,.getxattr= generic_getxattr,.listxattr= ext2_listxattr,.removexattr= generic_removexattr,#endif.setattr= ext2_setattr,.permission= ext2_permission,};