全部博文(46)
分类: 嵌入式
2010-05-04 08:47:26
}; struct file { /* * fu_list becomes invalid after file_free is called and queued via * fu_rcuhead for RCU freeing */ union { struct list_head fu_list; struct rcu_head fu_rcuhead; } f_u; struct path f_path; #define f_dentry f_path.dentry #define f_vfsmnt f_path.mnt const struct file_operations *f_op; atomic_t f_count; unsigned int f_flags; mode_t f_mode; loff_t f_pos; struct fown_struct f_owner; unsigned int f_uid, f_gid; struct file_ra_state f_ra; unsigned long f_version; #ifdef CONFIG_SECURITY void *f_security; #endif /* needed for tty driver, and maybe others */ void *private_data; #ifdef CONFIG_EPOLL /* Used by fs/eventpoll.c to link all the hooks to this file */ struct list_head f_ep_links; spinlock_t f_ep_lock; #endif /* #ifdef CONFIG_EPOLL */ struct address_space *f_mapping; }; 当访问文件时,首先open("",??),
open函数通过系统调用sys_open进入内核空间, sysopen又调用do_sys_open, long do_sys_open(int dfd, const char __user *filename, int flags, int mode) { char *tmp = getname(filename); int fd = PTR_ERR(tmp); if (!IS_ERR(tmp)) { fd = get_unused_fd(); if (fd >= 0) { struct file *f = do_filp_open(dfd, tmp, flags, mode); if (IS_ERR(f)) { put_unused_fd(fd); fd = PTR_ERR(f); } else { fsnotify_open(f->f_path.dentry); fd_install(fd, f); } } putname(tmp); } return fd; } int get_unused_fd(void) { struct files_struct * files = current->files; int fd, error; struct fdtable *fdt; error = -EMFILE; spin_lock(&files->file_lock); repeat: fdt = files_fdtable(files); fd = find_next_zero_bit(fdt->open_fds->fds_bits, fdt->max_fds, files->next_fd); /* * N.B. For clone tasks sharing a files structure, this test * will limit the total number of files that can be opened. */ if (fd >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur) goto out; /* Do we need to expand the fd array or fd set? */ error = expand_files(files, fd); if (error < 0) goto out; if (error) { /* * If we needed to expand the fs array we * might have blocked - try again. */ error = -EMFILE; goto repeat; } FD_SET(fd, fdt->open_fds); FD_CLR(fd, fdt->close_on_exec); files->next_fd = fd + 1; #if 1 /* Sanity check */ if (fdt->fd[fd] != NULL) { printk(KERN_WARNING "get_unused_fd: slot %d not NULL!\n", fd); fdt->fd[fd] = NULL; } #endif error = fd; out: spin_unlock(&files->file_lock); return error; } do_sys_open 通过get_unused_fd(),在当前进程空间内的struct file结构数组中, 找一个空的struct file{}结构,并返回一个数组的下标号, 之后do_sys_open又调用do_filp_open,do_filp_open调用nameidata_to_filp, nameidata_to_filp调用__dentry_open, static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags, struct file *f, int (*open)(struct inode *, struct file *)) { struct inode *inode; int error; f->f_flags = flags; f->f_mode = ((flags+1) & O_ACCMODE) | FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE; inode = dentry->d_inode; if (f->f_mode & FMODE_WRITE) { error = get_write_access(inode); if (error) goto cleanup_file; } f->f_mapping = inode->i_mapping; f->f_path.dentry = dentry; f->f_path.mnt = mnt; f->f_pos = 0; f->f_op = fops_get(inode->i_fop); file_move(f, &inode->i_sb->s_files); if (!open && f->f_op) open = f->f_op->open; if (open) { error = open(inode, f); if (error) goto cleanup_all; } f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC); file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping); /* NB: we're sure to have correct a_ops only after f_op->open */ if (f->f_flags & O_DIRECT) { if (!f->f_mapping->a_ops || ((!f->f_mapping->a_ops->direct_IO) && (!f->f_mapping->a_ops->get_xip_page))) { fput(f); f = ERR_PTR(-EINVAL); } } return f; cleanup_all: fops_put(f->f_op); if (f->f_mode & FMODE_WRITE) put_write_access(inode); file_kill(f); f->f_path.dentry = NULL; f->f_path.mnt = NULL; cleanup_file: put_filp(f); dput(dentry); mntput(mnt); return ERR_PTR(error); } struct inode { struct hlist_node i_hash; struct list_head i_list; struct list_head i_sb_list; struct list_head i_dentry; unsigned long i_ino; atomic_t i_count; unsigned int i_nlink; uid_t i_uid; gid_t i_gid; dev_t i_rdev; unsigned long i_version; loff_t i_size; #ifdef __NEED_I_SIZE_ORDERED seqcount_t i_size_seqcount; #endif struct timespec i_atime; struct timespec i_mtime; struct timespec i_ctime; unsigned int i_blkbits; blkcnt_t i_blocks; unsigned short i_bytes; umode_t i_mode; spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */ struct mutex i_mutex; struct rw_semaphore i_alloc_sem; struct inode_operations *i_op; const struct file_operations *i_fop; /* former ->i_op->default_file_ops */ struct super_block *i_sb; struct file_lock *i_flock; struct address_space *i_mapping; struct address_space i_data; #ifdef CONFIG_QUOTA struct dquot *i_dquot[MAXQUOTAS]; #endif struct list_head i_devices; union { struct pipe_inode_info *i_pipe; struct block_device *i_bdev; struct cdev *i_cdev; }; int i_cindex; __u32 i_generation; #ifdef CONFIG_DNOTIFY unsigned long i_dnotify_mask; /* Directory notify events */ struct dnotify_struct *i_dnotify; /* for directory notifications */ #endif #ifdef CONFIG_INOTIFY struct list_head inotify_watches; /* watches on this inode */ struct mutex inotify_mutex; /* protects the watches list */ #endif unsigned long i_state; unsigned long dirtied_when; /* jiffies of first dirtying */ unsigned int i_flags; atomic_t i_writecount; #ifdef CONFIG_SECURITY void *i_security; #endif void *i_private; /* fs or device private pointer */ }; #define fops_get(fops) \ (((fops) && try_module_get((fops)->owner) ? (fops) : NULL)) 我们一般加载模块 #else /*!CONFIG_MODULE_UNLOAD*/ static inline int try_module_get(struct module *module) { return !module || module_is_live(module); } 在__dentry_open,通过关键语句,f->f_op = fops_get(inode->i_fop); 得到了具有一个指向struct file_operations结构的指针的struct file结构指针,
之后通过语句 if (!open && f->f_op) open = f->f_op->open; if (open) { error = open(inode, f); if (error) goto cleanup_all; } 调用我们编写的struct file_operations中的xxxopen() 其他操作类似, read调用顺序如下: read()->sys_read()->vfs_read()->{file->f_op->read}
用户空间的read、write---linux系统调用---间接调用设备驱动程序中file_operations结构中的函数
整个调用过程是这样一个顺序的。