file.h

ARM 嵌入式 系统 设计与实例开发 实验教材 二源码

/*
 * Wrapper functions for accessing the file_struct fd array.
 */

#ifndef __LINUX_FILE_H
#define __LINUX_FILE_H

extern void FASTCALL(fput(struct file *));
extern struct file * FASTCALL(fget(unsigned int fd));
 
static inline int get_close_on_exec(unsigned int fd)
{
	struct files_struct *files = current->files;
	int res;
	read_lock(&files->file_lock);
	res = FD_ISSET(fd, files->close_on_exec);
	read_unlock(&files->file_lock);
	return res;
}

static inline void set_close_on_exec(unsigned int fd, int flag)
{
	struct files_struct *files = current->files;
	write_lock(&files->file_lock);
	if (flag)
		FD_SET(fd, files->close_on_exec);
	else
		FD_CLR(fd, files->close_on_exec);
	write_unlock(&files->file_lock);
}

static inline struct file * fcheck_files(struct files_struct *files, unsigned int fd)
{
	struct file * file = NULL;

	if (fd < files->max_fds)
		file = files->fd[fd];
	return file;
}

/*
 * Check whether the specified fd has an open file.
 */
static inline struct file * fcheck(unsigned int fd)
{
	struct file * file = NULL;
	struct files_struct *files = current->files;

	if (fd < files->max_fds)
		file = files->fd[fd];
	return file;
}

extern void put_filp(struct file *);

extern int get_unused_fd(void);

static inline void __put_unused_fd(struct files_struct *files, unsigned int fd)
{
	FD_CLR(fd, files->open_fds);
	if (fd < files->next_fd)
		files->next_fd = fd;
}

static inline void put_unused_fd(unsigned int fd)
{
	struct files_struct *files = current->files;

	write_lock(&files->file_lock);
	__put_unused_fd(files, fd);
	write_unlock(&files->file_lock);
}

/*
 * Install a file pointer in the fd array.  
 *
 * The VFS is full of places where we drop the files lock between
 * setting the open_fds bitmap and installing the file in the file
 * array.  At any such point, we are vulnerable to a dup2() race
 * installing a file in the array before us.  We need to detect this and
 * fput() the struct file we are about to overwrite in this case.
 *
 * It should never happen - if we allow dup2() do it, _really_ bad things
 * will follow.
 */

static inline void fd_install(unsigned int fd, struct file * file)
{
	struct files_struct *files = current->files;
	
	write_lock(&files->file_lock);
	if (files->fd[fd])
		BUG();
	files->fd[fd] = file;
	write_unlock(&files->file_lock);
}

void put_files_struct(struct files_struct *fs);

#endif /* __LINUX_FILE_H */