file-open-driver.rar_linux 打开 文件_open

#include <linux/namei.h> //filename: "/dev/rtc" char * getname(const char __user * filename) { char *tmp, *result; result = ERR_PTR(-ENOMEM); tmp = __getname(); //分配内存用于存储文件的路径名 if (tmp) { int retval = do_getname(filename, tmp);//调完后:tmp="/dev/rtc" result = tmp; if (retval < 0) { __putname(tmp); result = ERR_PTR(retval); } } //... ... return result; } static int do_getname(const char __user *filename, char *page) { int retval; unsigned long len = PATH_MAX; //... ... retval = strncpy_from_user(page, filename, len);//filename ==>page if (retval > 0) { if (retval < len) return 0; return -ENAMETOOLONG; } else if (!retval) retval = -ENOENT; return retval; } /* * open_namei() * * namei for open - this is in fact almost the whole open-routine. * * Note that the low bits of "flag" aren't the same as in the open * system call - they are 00 - no permissions needed * 01 - read permission needed * 10 - write permission needed * 11 - read/write permissions needed * which is a lot more logical, and also allows the "no perm" needed * for symlinks (where the permissions are checked later). * SMP-safe */ int open_namei(..., const char *pathname, int flag, int mode, struct nameidata *nd) { int acc_mode, error; struct path path; struct dentry *dir; int count = 0; //... ... if (flag & O_TRUNC) acc_mode |= MAY_WRITE; if (flag & O_APPEND) acc_mode |= MAY_APPEND; /* * The simplest case - just a plain lookup. */ if (!(flag & O_CREAT)) {//若文件存在则打开，不存在则出错而不创建 // 找到此文件 后，将相关信息写入nd error = path_lookup_open(..., pathname, lookup_flags(flag), nd, flag); if (error) return error; goto ok; } //若文件存在则打开，不存在则创建,找到后或创建了 //将相关信息写入nd error = path_lookup_create(...,pathname,LOOKUP_PARENT,nd,flag,mode); if (error) return error; error = -EISDIR; if (nd->last_type != LAST_NORM || ...) //打开的是个目录而非文件 goto exit; dir = nd->dentry; nd->flags &= ~LOOKUP_PARENT; mutex_lock(&dir->d_inode->i_mutex);//文件 已找到或已创建，对其加锁开始操作 path.dentry = lookup_hash(nd); path.mnt = nd->mnt; //... ... /* * It already exists. */ mutex_unlock(&dir->d_inode->i_mutex); //... ... ok: error = may_open(nd, acc_mode, flag); if (error) goto exit; return 0; // ... ... exit: //... ... return error; // ... ... } int may_open(struct nameidata *nd, int acc_mode, int flag) { struct dentry *dentry = nd->dentry; struct inode *inode = dentry->d_inode; int error; if (!inode) return -ENOENT; if (S_ISLNK(inode->i_mode)) return -ELOOP; if (S_ISDIR(inode->i_mode) && (flag & FMODE_WRITE)) //目录无法本身是无法写入 return -EISDIR; error = vfs_permission(nd, acc_mode); if (error) return error; /* * FIFO's, sockets and device files are special: they don't * actually live on the filesystem itself, and as such you * can write to them even if the filesystem is read-only. */ if (S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) { flag &= ~O_TRUNC; } else if (S_ISBLK(inode->i_mode) || S_ISCHR(inode->i_mode)) { if (nd->mnt->mnt_flags & MNT_NODEV) return -EACCES; flag &= ~O_TRUNC; } else if (IS_RDONLY(inode) && (flag & FMODE_WRITE)) //只读文件 不能写 return -EROFS; /* * An append-only file must be opened in append mode for writing. */ if (IS_APPEND(inode)) { //... ... if (flag & O_TRUNC) return -EPERM; } //... ... if (flag & O_TRUNC) { error = get_write_access(inode); if (error) return error; //... ... } else //... ... return 0; } //首先nd设置为起始目录的相关信息，路径以/号分隔，从路径中 //分享出一个目录项，然后到nd->dentry的子目录项中去搜索 //如果找到了调用path_to_nameidata()让nd前进一步 static inline void path_to_nameidata(struct path *path, struct nameidata *nd) { dput(nd->dentry);//老的释放 //... ... nd->mnt = path->mnt; nd->dentry = path->dentry;//推进一步 } static inline int lookup_flags(unsigned int f) { unsigned long retval = LOOKUP_FOLLOW; if (f & O_NOFOLLOW) retval &= ~LOOKUP_FOLLOW; if (f & O_DIRECTORY) retval |= LOOKUP_DIRECTORY; return retval; } int get_write_access(struct inode * inode) { spin_lock(&inode->i_lock); if (atomic_read(&inode->i_writecount) < 0) { spin_unlock(&inode->i_lock); return -ETXTBSY; } atomic_inc(&inode->i_writecount); spin_unlock(&inode->i_lock); return 0; } int vfs_permission(struct nameidata *nd, int mask) { return permission(nd->dentry->d_inode, mask, nd); } int permission(struct inode *inode, int mask, struct nameidata *nd) { int retval; //... ... if (inode->i_op && inode->i_op->permission) retval = inode->i_op->permission(inode, ..., nd); else retval = generic_permission(inode, ..., NULL); if (retval) return retval; ... ... } /** * path_lookup_open - lookup a file path with open intent * @dfd: the directory to use as base, or AT_FDCWD * @name: pointer to file name * @lookup_flags: lookup intent flags * @nd: pointer to nameidata * @open_flags: open intent flags */ //name: "/dev/rtc" //open_flags: O_RDONLY int path_lookup_open(..., const char *name, unsigned int lookup_flags, struct nameidata *nd, int open_flags) { return __path_lookup_intent_open(..., name, lookup_flags, nd, open_flags, 0); } static int __path_lookup_intent_open(..., const char *name, unsigned int lookup_flags, struct nameidata *nd, int open_flags, int create_mode) { int err; //... ... err = do_path_lookup(..., name, lookup_flags|LOOKUP_OPEN, nd); if (IS_ERR(nd->intent.open.file)) { //处理错误 } //... return err; } /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */ //name: "/dev/rtc" //flags: O_RDONLY|LOOKUP_OPEN static int fastcall do_path_lookup(..., const char *name, unsigned int flags, struct nameidata *nd) { int retval = 0; int fput_needed; struct file *file; struct fs_struct *fs = current->fs;//拿到当前进程所在的文件系统数据结构 //init nd{} nd->last_type = LAST_ROOT; /* if there are only slashes... */ nd->flags = flags; nd->depth = 0; if (*name=='/') {//"/dev/rtc" ==>以"/"开头的是绝对路径 read_lock(&fs->lock); //... ... nd->mnt = mntget(fs->rootmnt); nd->dentry = dget(fs->root); read_unlock(&fs->lock); } else if (dfd == AT_FDCWD) { //"./rtc" |"rtc/"==>用相对当前路径 read_lock(&fs->lock); nd->mnt = mntget(fs->pwdmnt); nd->dentry = dget(fs->pwd); read_unlock(&fs->lock); } else { //... ... } current->total_link_count = 0; retval = link_path_walk(name, nd); //... ... } int fastcall link_path_walk(const char *name, struct nameidata *nd) { struct nameidata save = *nd; int result; //... ... result = __link_path_walk(name, nd); //... ... return result; } /* * Name resolution. * This is the basic name resolution function, turning a pathname into * the final dentry. We expect 'base' to be positive and a directory. * * Returns 0 and nd will have valid dentry and mnt on success. * Returns error and drops reference to input namei data on failure. */ //name:/dev/rtc //nd:当前进程所在的文件系统的绝对路径对应的信息:目录项及挂载点 static fastcall int __link_path_walk(const char * name, struct nameidata *nd) { struct path next; struct inode *inode; int err; unsigned int lookup_flags = nd->flags; while (*name=='/') // ==>//////dev/rtc ==> OK name++; if (!*name) //==>////////// goto return_reval; inode = nd->dentry->d_inode; //... ...