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