kernel/kfifo.c

   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  */
  39 struct 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 }
  58 EXPORT_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  */
  68 struct 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 }
  93 EXPORT_SYMBOL(kfifo_alloc);
  94
  95 /**
  96  * kfifo_free - frees the FIFO
  97  * @fifo: the fifo to be freed.
  98  */
  99 void kfifo_free(struct kfifo *fifo)
 100 {
 101         kfree(fifo->buffer);
 102         kfree(fifo);
 103 }
 104 EXPORT_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  */
 119 unsigned 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 }
 151 EXPORT_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  */
 165 unsigned 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 }
 197 EXPORT_SYMBOL(__kfifo_get);