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Linux/include/linux/posix-clock.h

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  1 /*
  2  * posix-clock.h - support for dynamic clock devices
  3  *
  4  * Copyright (C) 2010 OMICRON electronics GmbH
  5  *
  6  *  This program is free software; you can redistribute it and/or modify
  7  *  it under the terms of the GNU General Public License as published by
  8  *  the Free Software Foundation; either version 2 of the License, or
  9  *  (at your option) any later version.
 10  *
 11  *  This program is distributed in the hope that it will be useful,
 12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 14  *  GNU General Public License for more details.
 15  *
 16  *  You should have received a copy of the GNU General Public License
 17  *  along with this program; if not, write to the Free Software
 18  *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 19  */
 20 #ifndef _LINUX_POSIX_CLOCK_H_
 21 #define _LINUX_POSIX_CLOCK_H_
 22 
 23 #include <linux/cdev.h>
 24 #include <linux/fs.h>
 25 #include <linux/poll.h>
 26 #include <linux/posix-timers.h>
 27 #include <linux/rwsem.h>
 28 
 29 struct posix_clock;
 30 
 31 /**
 32  * struct posix_clock_operations - functional interface to the clock
 33  *
 34  * Every posix clock is represented by a character device. Drivers may
 35  * optionally offer extended capabilities by implementing the
 36  * character device methods. The character device file operations are
 37  * first handled by the clock device layer, then passed on to the
 38  * driver by calling these functions.
 39  *
 40  * @owner:          The clock driver should set to THIS_MODULE
 41  * @clock_adjtime:  Adjust the clock
 42  * @clock_gettime:  Read the current time
 43  * @clock_getres:   Get the clock resolution
 44  * @clock_settime:  Set the current time value
 45  * @open:           Optional character device open method
 46  * @release:        Optional character device release method
 47  * @ioctl:          Optional character device ioctl method
 48  * @read:           Optional character device read method
 49  * @poll:           Optional character device poll method
 50  */
 51 struct posix_clock_operations {
 52         struct module *owner;
 53 
 54         int  (*clock_adjtime)(struct posix_clock *pc, struct timex *tx);
 55 
 56         int  (*clock_gettime)(struct posix_clock *pc, struct timespec64 *ts);
 57 
 58         int  (*clock_getres) (struct posix_clock *pc, struct timespec64 *ts);
 59 
 60         int  (*clock_settime)(struct posix_clock *pc,
 61                               const struct timespec64 *ts);
 62 
 63         /*
 64          * Optional character device methods:
 65          */
 66         long    (*ioctl)   (struct posix_clock *pc,
 67                             unsigned int cmd, unsigned long arg);
 68 
 69         int     (*open)    (struct posix_clock *pc, fmode_t f_mode);
 70 
 71         __poll_t (*poll)   (struct posix_clock *pc,
 72                             struct file *file, poll_table *wait);
 73 
 74         int     (*release) (struct posix_clock *pc);
 75 
 76         ssize_t (*read)    (struct posix_clock *pc,
 77                             uint flags, char __user *buf, size_t cnt);
 78 };
 79 
 80 /**
 81  * struct posix_clock - represents a dynamic posix clock
 82  *
 83  * @ops:     Functional interface to the clock
 84  * @cdev:    Character device instance for this clock
 85  * @kref:    Reference count.
 86  * @rwsem:   Protects the 'zombie' field from concurrent access.
 87  * @zombie:  If 'zombie' is true, then the hardware has disappeared.
 88  * @release: A function to free the structure when the reference count reaches
 89  *           zero. May be NULL if structure is statically allocated.
 90  *
 91  * Drivers should embed their struct posix_clock within a private
 92  * structure, obtaining a reference to it during callbacks using
 93  * container_of().
 94  */
 95 struct posix_clock {
 96         struct posix_clock_operations ops;
 97         struct cdev cdev;
 98         struct kref kref;
 99         struct rw_semaphore rwsem;
100         bool zombie;
101         void (*release)(struct posix_clock *clk);
102 };
103 
104 /**
105  * posix_clock_register() - register a new clock
106  * @clk:   Pointer to the clock. Caller must provide 'ops' and 'release'
107  * @devid: Allocated device id
108  *
109  * A clock driver calls this function to register itself with the
110  * clock device subsystem. If 'clk' points to dynamically allocated
111  * memory, then the caller must provide a 'release' function to free
112  * that memory.
113  *
114  * Returns zero on success, non-zero otherwise.
115  */
116 int posix_clock_register(struct posix_clock *clk, dev_t devid);
117 
118 /**
119  * posix_clock_unregister() - unregister a clock
120  * @clk: Clock instance previously registered via posix_clock_register()
121  *
122  * A clock driver calls this function to remove itself from the clock
123  * device subsystem. The posix_clock itself will remain (in an
124  * inactive state) until its reference count drops to zero, at which
125  * point it will be deallocated with its 'release' method.
126  */
127 void posix_clock_unregister(struct posix_clock *clk);
128 
129 #endif
130 

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