include/linux/kfifo.h

   1 /*
   2  * A generic kernel FIFO implementation.
   3  *
   4  * Copyright (C) 2009 Stefani Seibold <stefani@seibold.net>
   5  * Copyright (C) 2004 Stelian Pop <stelian@popies.net>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20  *
  21  */
  22
  23 /*
  24  * Howto porting drivers to the new generic fifo API:
  25  *
  26  * - Modify the declaration of the "struct kfifo *" object into a
  27  *   in-place "struct kfifo" object
  28  * - Init the in-place object with kfifo_alloc() or kfifo_init()
  29  *   Note: The address of the in-place "struct kfifo" object must be
  30  *   passed as the first argument to this functions
  31  * - Replace the use of __kfifo_put into kfifo_in and __kfifo_get
  32  *   into kfifo_out
  33  * - Replace the use of kfifo_put into kfifo_in_locked and kfifo_get
  34  *   into kfifo_out_locked
  35  *   Note: the spinlock pointer formerly passed to kfifo_init/kfifo_alloc
  36  *   must be passed now to the kfifo_in_locked and kfifo_out_locked
  37  *   as the last parameter.
  38  * - All formerly name __kfifo_* functions has been renamed into kfifo_*
  39  */
  40
  41 #ifndef _LINUX_KFIFO_H
  42 #define _LINUX_KFIFO_H
  43
  44 #include <linux/kernel.h>
  45 #include <linux/spinlock.h>
  46
  47 struct kfifo {
  48         unsigned char *buffer;  /* the buffer holding the data */
  49         unsigned int size;      /* the size of the allocated buffer */
  50         unsigned int in;        /* data is added at offset (in % size) */
  51         unsigned int out;       /* data is extracted from off. (out % size) */
  52 };
  53
  54 extern void kfifo_init(struct kfifo *fifo, unsigned char *buffer,
  55                         unsigned int size);
  56 extern __must_check int kfifo_alloc(struct kfifo *fifo, unsigned int size,
  57                         gfp_t gfp_mask);
  58 extern void kfifo_free(struct kfifo *fifo);
  59 extern unsigned int kfifo_in(struct kfifo *fifo,
  60                                 const unsigned char *from, unsigned int len);
  61 extern __must_check unsigned int kfifo_out(struct kfifo *fifo,
  62                                 unsigned char *to, unsigned int len);
  63
  64 /**
  65  * kfifo_reset - removes the entire FIFO contents
  66  * @fifo: the fifo to be emptied.
  67  */
  68 static inline void kfifo_reset(struct kfifo *fifo)
  69 {
  70         fifo->in = fifo->out = 0;
  71 }
  72
  73 /**
  74  * kfifo_len - returns the number of used bytes in the FIFO
  75  * @fifo: the fifo to be used.
  76  */
  77 static inline unsigned int kfifo_len(struct kfifo *fifo)
  78 {
  79         register unsigned int   out;
  80
  81         out = fifo->out;
  82         smp_rmb();
  83         return fifo->in - out;
  84 }
  85
  86 /**
  87  * kfifo_in_locked - puts some data into the FIFO using a spinlock for locking
  88  * @fifo: the fifo to be used.
  89  * @from: the data to be added.
  90  * @n: the length of the data to be added.
  91  * @lock: pointer to the spinlock to use for locking.
  92  *
  93  * This function copies at most @len bytes from the @from buffer into
  94  * the FIFO depending on the free space, and returns the number of
  95  * bytes copied.
  96  */
  97 static inline unsigned int kfifo_in_locked(struct kfifo *fifo,
  98                 const unsigned char *from, unsigned int n, spinlock_t *lock)
  99 {
 100         unsigned long flags;
 101         unsigned int ret;
 102
 103         spin_lock_irqsave(lock, flags);
 104
 105         ret = kfifo_in(fifo, from, n);
 106
 107         spin_unlock_irqrestore(lock, flags);
 108
 109         return ret;
 110 }
 111
 112 /**
 113  * kfifo_out_locked - gets some data from the FIFO using a spinlock for locking
 114  * @fifo: the fifo to be used.
 115  * @to: where the data must be copied.
 116  * @n: the size of the destination buffer.
 117  * @lock: pointer to the spinlock to use for locking.
 118  *
 119  * This function copies at most @len bytes from the FIFO into the
 120  * @to buffer and returns the number of copied bytes.
 121  */
 122 static inline __must_check unsigned int kfifo_out_locked(struct kfifo *fifo,
 123         unsigned char *to, unsigned int n, spinlock_t *lock)
 124 {
 125         unsigned long flags;
 126         unsigned int ret;
 127
 128         spin_lock_irqsave(lock, flags);
 129
 130         ret = kfifo_out(fifo, to, n);
 131
 132         /*
 133          * optimization: if the FIFO is empty, set the indices to 0
 134          * so we don't wrap the next time
 135          */
 136         if (fifo->in == fifo->out)
 137                 fifo->in = fifo->out = 0;
 138
 139         spin_unlock_irqrestore(lock, flags);
 140
 141         return ret;
 142 }
 143
 144 #endif