Documentation: filesystems: updated struct file_operations documentation in vfs.txt

----------------------

This describes how the VFS can manipulate an open file. As of kernel

3.12, the following members are defined:

4.1, the following members are defined:

struct file_operations {

	struct module *owner;

	long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);

	long (*compat_ioctl) (struct file *, unsigned int, unsigned long);

	int (*mmap) (struct file *, struct vm_area_struct *);

	int (*mremap)(struct file *, struct vm_area_struct *);

	int (*open) (struct inode *, struct file *);

	int (*flush) (struct file *);

	int (*flush) (struct file *, fl_owner_t id);

	int (*release) (struct inode *, struct file *);

	int (*fsync) (struct file *, loff_t, loff_t, int datasync);

	int (*aio_fsync) (struct kiocb *, int datasync);

	unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);

	int (*check_flags)(int);

	int (*flock) (struct file *, int, struct file_lock *);

	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, size_t, unsigned int);

	ssize_t (*splice_read)(struct file *, struct pipe_inode_info *, size_t, unsigned int);

	int (*setlease)(struct file *, long arg, struct file_lock **, void **);

	long (*fallocate)(struct file *, int mode, loff_t offset, loff_t len);

	ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);

	ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);

	int (*setlease)(struct file *, long, struct file_lock **, void **);

	long (*fallocate)(struct file *file, int mode, loff_t offset,

			  loff_t len);

	void (*show_fdinfo)(struct seq_file *m, struct file *f);

#ifndef CONFIG_MMU

	unsigned (*mmap_capabilities)(struct file *);

#endif

};

Again, all methods are called without any locks being held, unless