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