kernel/kfifo.c

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