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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  */
kfifo_init(unsigned char * buffer,unsigned int size,gfp_t gfp_mask,spinlock_t * lock)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  */
kfifo_alloc(unsigned int size,gfp_t gfp_mask,spinlock_t * lock)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  */
kfifo_free(struct kfifo * fifo)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  */
__kfifo_put(struct kfifo * fifo,unsigned char * buffer,unsigned int len)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  */
__kfifo_get(struct kfifo * fifo,unsigned char * buffer,unsigned int len)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);
198