linux/kernel/kfifo.c
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   1/*
   2 * A simple kernel FIFO implementation.
   3 *
   4 * Copyright (C) 2004 Stelian Pop <stelian@popies.net>
   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 */
  21
  22#include <linux/kernel.h>
  23#include <linux/module.h>
  24#include <linux/slab.h>
  25#include <linux/err.h>
  26#include <linux/kfifo.h>
  27#include <linux/log2.h>
  28
  29/**
  30 * kfifo_init - allocates a new FIFO using a preallocated buffer
  31 * @buffer: the preallocated buffer to be used.
  32 * @size: the size of the internal buffer, this have to be a power of 2.
  33 * @gfp_mask: get_free_pages mask, passed to kmalloc()
  34 * @lock: the lock to be used to protect the fifo buffer
  35 *
  36 * Do NOT pass the kfifo to kfifo_free() after use! Simply free the
  37 * &struct kfifo with kfree().
  38 */
  39struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size,
  40                         gfp_t gfp_mask, spinlock_t *lock)
  41{
  42        struct kfifo *fifo;
  43
  44        /* size must be a power of 2 */
  45        BUG_ON(!is_power_of_2(size));
  46
  47        fifo = kmalloc(sizeof(struct kfifo), gfp_mask);
  48        if (!fifo)
  49                return ERR_PTR(-ENOMEM);
  50
  51        fifo->buffer = buffer;
  52        fifo->size = size;
  53        fifo->in = fifo->out = 0;
  54        fifo->lock = lock;
  55
  56        return fifo;
  57}
  58EXPORT_SYMBOL(kfifo_init);
  59
  60/**
  61 * kfifo_alloc - allocates a new FIFO and its internal buffer
  62 * @size: the size of the internal buffer to be allocated.
  63 * @gfp_mask: get_free_pages mask, passed to kmalloc()
  64 * @lock: the lock to be used to protect the fifo buffer
  65 *
  66 * The size will be rounded-up to a power of 2.
  67 */
  68struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask, spinlock_t *lock)
  69{
  70        unsigned char *buffer;
  71        struct kfifo *ret;
  72
  73        /*
  74         * round up to the next power of 2, since our 'let the indices
  75         * wrap' tachnique works only in this case.
  76         */
  77        if (size & (size - 1)) {
  78                BUG_ON(size > 0x80000000);
  79                size = roundup_pow_of_two(size);
  80        }
  81
  82        buffer = kmalloc(size, gfp_mask);
  83        if (!buffer)
  84                return ERR_PTR(-ENOMEM);
  85
  86        ret = kfifo_init(buffer, size, gfp_mask, lock);
  87
  88        if (IS_ERR(ret))
  89                kfree(buffer);
  90
  91        return ret;
  92}
  93EXPORT_SYMBOL(kfifo_alloc);
  94
  95/**
  96 * kfifo_free - frees the FIFO
  97 * @fifo: the fifo to be freed.
  98 */
  99void kfifo_free(struct kfifo *fifo)
 100{
 101        kfree(fifo->buffer);
 102        kfree(fifo);
 103}
 104EXPORT_SYMBOL(kfifo_free);
 105
 106/**
 107 * __kfifo_put - puts some data into the FIFO, no locking version
 108 * @fifo: the fifo to be used.
 109 * @buffer: the data to be added.
 110 * @len: the length of the data to be added.
 111 *
 112 * This function copies at most @len bytes from the @buffer into
 113 * the FIFO depending on the free space, and returns the number of
 114 * bytes copied.
 115 *
 116 * Note that with only one concurrent reader and one concurrent
 117 * writer, you don't need extra locking to use these functions.
 118 */
 119unsigned int __kfifo_put(struct kfifo *fifo,
 120                         unsigned char *buffer, unsigned int len)
 121{
 122        unsigned int l;
 123
 124        len = min(len, fifo->size - fifo->in + fifo->out);
 125
 126        /*
 127         * Ensure that we sample the fifo->out index -before- we
 128         * start putting bytes into the kfifo.
 129         */
 130
 131        smp_mb();
 132
 133        /* first put the data starting from fifo->in to buffer end */
 134        l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
 135        memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l);
 136
 137        /* then put the rest (if any) at the beginning of the buffer */
 138        memcpy(fifo->buffer, buffer + l, len - l);
 139
 140        /*
 141         * Ensure that we add the bytes to the kfifo -before-
 142         * we update the fifo->in index.
 143         */
 144
 145        smp_wmb();
 146
 147        fifo->in += len;
 148
 149        return len;
 150}
 151EXPORT_SYMBOL(__kfifo_put);
 152
 153/**
 154 * __kfifo_get - gets some data from the FIFO, no locking version
 155 * @fifo: the fifo to be used.
 156 * @buffer: where the data must be copied.
 157 * @len: the size of the destination buffer.
 158 *
 159 * This function copies at most @len bytes from the FIFO into the
 160 * @buffer and returns the number of copied bytes.
 161 *
 162 * Note that with only one concurrent reader and one concurrent
 163 * writer, you don't need extra locking to use these functions.
 164 */
 165unsigned int __kfifo_get(struct kfifo *fifo,
 166                         unsigned char *buffer, unsigned int len)
 167{
 168        unsigned int l;
 169
 170        len = min(len, fifo->in - fifo->out);
 171
 172        /*
 173         * Ensure that we sample the fifo->in index -before- we
 174         * start removing bytes from the kfifo.
 175         */
 176
 177        smp_rmb();
 178
 179        /* first get the data from fifo->out until the end of the buffer */
 180        l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));
 181        memcpy(buffer, fifo->buffer + (fifo->out & (fifo->size - 1)), l);
 182
 183        /* then get the rest (if any) from the beginning of the buffer */
 184        memcpy(buffer + l, fifo->buffer, len - l);
 185
 186        /*
 187         * Ensure that we remove the bytes from the kfifo -before-
 188         * we update the fifo->out index.
 189         */
 190
 191        smp_mb();
 192
 193        fifo->out += len;
 194
 195        return len;
 196}
 197EXPORT_SYMBOL(__kfifo_get);
 198
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