title: What are the "struct file_operations" arguments?
body: <p>I'm implementing a Linux character device driver.</p>
  
  <p>The linux/fs.h header file lists the file_operations without argument names.</p>
  
  <p>e.g.</p>
  
  <pre><code>struct file_operations {
      struct module *owner;
      loff_t (*llseek) (struct file *, loff_t, int);
      ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
      ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
      ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
      ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
      int (*readdir) (struct file *, void *, filldir_t);
      unsigned int (*poll) (struct file *, struct poll_table_struct *);
      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 (*open) (struct inode *, 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);
      int (*fasync) (int, struct file *, int);
      int (*lock) (struct file *, int, struct file_lock *);
      ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
      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 *, 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 **);
      long (*fallocate)(struct file *file, int mode, loff_t offset,
                loff_t len);
  };
  </code></pre>
  
  <p>Where is the documentation that tells me what each argument is? Some are sort-of obvious, but some aren't. I prefer to refer to official documentation if I can, but I just can't find it.</p>
  
  <p>e.g.</p>
  
  <pre><code>int (*fsync) (struct file *, loff_t, loff_t, int datasync);
  </code></pre>
  
  <p>There are two loff_t arguments. How do I know what they do?</p>
  
  <p>I've been Googling and reading the device driver book, but I can't find any documents that explain what the arguments are for. Some of the arguments have also changed from when LDD3 was written. </p>