text: /*
   * posix-clock.h - support for dynamic clock devices
   *
   * Copyright (C) 2010 OMICRON electronics GmbH
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License as published by
   *  the Free Software Foundation; either version 2 of the License, or
   *  (at your option) any later version.
   *
   *  This program is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *  GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License
   *  along with this program; if not, write to the Free Software
   *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   */
  #ifndef _LINUX_POSIX_CLOCK_H_
  #define _LINUX_POSIX_CLOCK_H_
  
  #include <linux/cdev.h>
  #include <linux/fs.h>
  #include <linux/poll.h>
  #include <linux/posix-timers.h>
  #include <linux/rwsem.h>
  
  struct posix_clock;
  
  /**
   * struct posix_clock_operations - functional interface to the clock
   *
   * Every posix clock is represented by a character device. Drivers may
   * optionally offer extended capabilities by implementing the
   * character device methods. The character device file operations are
   * first handled by the clock device layer, then passed on to the
   * driver by calling these functions.
   *
   * @owner:          The clock driver should set to THIS_MODULE
   * @clock_adjtime:  Adjust the clock
   * @clock_gettime:  Read the current time
   * @clock_getres:   Get the clock resolution
   * @clock_settime:  Set the current time value
   * @open:           Optional character device open method
   * @release:        Optional character device release method
   * @ioctl:          Optional character device ioctl method
   * @read:           Optional character device read method
   * @poll:           Optional character device poll method
   */
  struct posix_clock_operations {
  	struct module *owner;
  
  	int  (*clock_adjtime)(struct posix_clock *pc, struct timex *tx);
  
  	int  (*clock_gettime)(struct posix_clock *pc, struct timespec64 *ts);
  
  	int  (*clock_getres) (struct posix_clock *pc, struct timespec64 *ts);
  
  	int  (*clock_settime)(struct posix_clock *pc,
  			      const struct timespec64 *ts);
  
  	/*
  	 * Optional character device methods:
  	 */
  	long    (*ioctl)   (struct posix_clock *pc,
  			    unsigned int cmd, unsigned long arg);
  
  	int     (*open)    (struct posix_clock *pc, fmode_t f_mode);
  
  	uint    (*poll)    (struct posix_clock *pc,
  			    struct file *file, poll_table *wait);
  
  	int     (*release) (struct posix_clock *pc);
  
  	ssize_t (*read)    (struct posix_clock *pc,
  			    uint flags, char __user *buf, size_t cnt);
  };
  
  /**
   * struct posix_clock - represents a dynamic posix clock
   *
   * @ops:     Functional interface to the clock
   * @cdev:    Character device instance for this clock
   * @kref:    Reference count.
   * @rwsem:   Protects the 'zombie' field from concurrent access.
   * @zombie:  If 'zombie' is true, then the hardware has disappeared.
   * @release: A function to free the structure when the reference count reaches
   *           zero. May be NULL if structure is statically allocated.
   *
   * Drivers should embed their struct posix_clock within a private
   * structure, obtaining a reference to it during callbacks using
   * container_of().
   */
  struct posix_clock {
  	struct posix_clock_operations ops;
  	struct cdev cdev;
  	struct kref kref;
  	struct rw_semaphore rwsem;
  	bool zombie;
  	void (*release)(struct posix_clock *clk);
  };
  
  /**
   * posix_clock_register() - register a new clock
   * @clk:   Pointer to the clock. Caller must provide 'ops' and 'release'
   * @devid: Allocated device id
   *
   * A clock driver calls this function to register itself with the
   * clock device subsystem. If 'clk' points to dynamically allocated
   * memory, then the caller must provide a 'release' function to free
   * that memory.
   *
   * Returns zero on success, non-zero otherwise.
   */
  int posix_clock_register(struct posix_clock *clk, dev_t devid);
  
  /**
   * posix_clock_unregister() - unregister a clock
   * @clk: Clock instance previously registered via posix_clock_register()
   *
   * A clock driver calls this function to remove itself from the clock
   * device subsystem. The posix_clock itself will remain (in an
   * inactive state) until its reference count drops to zero, at which
   * point it will be deallocated with its 'release' method.
   */
  void posix_clock_unregister(struct posix_clock *clk);
  
  #endif
  