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本帖最后由 txgc_wm 于 2013-06-29 16:33 编辑
先上内核循环缓冲结构体的定义:- struct kfifo {
- unsigned char *buffer; /* the buffer holding the data */
- unsigned int size; /* the size of the allocated buffer */
- unsigned int in; /* data is added at offset (in % size) */
- unsigned int out; /* data is extracted from off. (out % size) */
- spinlock_t *lock; /* protects concurrent modifications */
- };
复制代码 如果对“Linux内核中的循环缓冲区”不是很了解的话,可以先参考这里。
对于结构体内的in和out两个变量,内核是作如下处理的:1、在读入数据时增加in;2、在取出数据时增加out;3、当检测到两个相等的时候将它们复位归0。1和2不作讨论和分析,针对第3点的处理,内核代码如下:- static inline unsigned int kfifo_get(struct kfifo *fifo,
- unsigned char *buffer, unsigned int len)
- {
- unsigned long flags;
- unsigned int ret;
- spin_lock_irqsave(fifo->lock, flags);
- ret = __kfifo_get(fifo, buffer, len);
- /*
- * optimization: if the FIFO is empty, set the indices to 0
- * so we don't wrap the next time
- */
- if (fifo->in == fifo->out)
- fifo->in = fifo->out = 0;
- spin_unlock_irqrestore(fifo->lock, flags);
- return ret;
- }
复制代码 问题:当数据写入速度大于读取速度的时候,in和out的值将永远不会相等,也就是说buffer永远是有数据的,这样的话in和out都存在超出自身数值表示范围,从而导致错误?
针对这个问题,不知大家有什么好的建议?
问题已解决,参考这里。
以下是摘自内核版本2.6.32.61的源码部分:- /*
- * A simple kernel FIFO implementation.
- *
- * Copyright (C) 2004 Stelian Pop <stelian@popies.net>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- *
- */
- #ifndef _LINUX_KFIFO_H
- #define _LINUX_KFIFO_H
- #include <linux/kernel.h>
- #include <linux/spinlock.h>
- struct kfifo {
- unsigned char *buffer; /* the buffer holding the data */
- unsigned int size; /* the size of the allocated buffer */
- unsigned int in; /* data is added at offset (in % size) */
- unsigned int out; /* data is extracted from off. (out % size) */
- spinlock_t *lock; /* protects concurrent modifications */
- };
- extern struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size,
- gfp_t gfp_mask, spinlock_t *lock);
- extern struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask,
- spinlock_t *lock);
- extern void kfifo_free(struct kfifo *fifo);
- extern unsigned int __kfifo_put(struct kfifo *fifo,
- const unsigned char *buffer, unsigned int len);
- extern unsigned int __kfifo_get(struct kfifo *fifo,
- unsigned char *buffer, unsigned int len);
- /**
- * __kfifo_reset - removes the entire FIFO contents, no locking version
- * @fifo: the fifo to be emptied.
- */
- static inline void __kfifo_reset(struct kfifo *fifo)
- {
- fifo->in = fifo->out = 0;
- }
- /**
- * kfifo_reset - removes the entire FIFO contents
- * @fifo: the fifo to be emptied.
- */
- static inline void kfifo_reset(struct kfifo *fifo)
- {
- unsigned long flags;
- spin_lock_irqsave(fifo->lock, flags);
- __kfifo_reset(fifo);
- spin_unlock_irqrestore(fifo->lock, flags);
- }
- /**
- * kfifo_put - puts some data into the FIFO
- * @fifo: the fifo to be used.
- * @buffer: the data to be added.
- * @len: the length of the data to be added.
- *
- * This function copies at most @len bytes from the @buffer into
- * the FIFO depending on the free space, and returns the number of
- * bytes copied.
- */
- static inline unsigned int kfifo_put(struct kfifo *fifo,
- const unsigned char *buffer, unsigned int len)
- {
- unsigned long flags;
- unsigned int ret;
- spin_lock_irqsave(fifo->lock, flags);
- ret = __kfifo_put(fifo, buffer, len);
- spin_unlock_irqrestore(fifo->lock, flags);
- return ret;
- }
- /**
- * kfifo_get - gets some data from the FIFO
- * @fifo: the fifo to be used.
- * @buffer: where the data must be copied.
- * @len: the size of the destination buffer.
- *
- * This function copies at most @len bytes from the FIFO into the
- * @buffer and returns the number of copied bytes.
- */
- static inline unsigned int kfifo_get(struct kfifo *fifo,
- unsigned char *buffer, unsigned int len)
- {
- unsigned long flags;
- unsigned int ret;
- spin_lock_irqsave(fifo->lock, flags);
- ret = __kfifo_get(fifo, buffer, len);
- /*
- * optimization: if the FIFO is empty, set the indices to 0
- * so we don't wrap the next time
- */
- if (fifo->in == fifo->out)
- fifo->in = fifo->out = 0;
- spin_unlock_irqrestore(fifo->lock, flags);
- return ret;
- }
- /**
- * __kfifo_len - returns the number of bytes available in the FIFO, no locking version
- * @fifo: the fifo to be used.
- */
- static inline unsigned int __kfifo_len(struct kfifo *fifo)
- {
- return fifo->in - fifo->out;
- }
- /**
- * kfifo_len - returns the number of bytes available in the FIFO
- * @fifo: the fifo to be used.
- */
- static inline unsigned int kfifo_len(struct kfifo *fifo)
- {
- unsigned long flags;
- unsigned int ret;
- spin_lock_irqsave(fifo->lock, flags);
- ret = __kfifo_len(fifo);
- spin_unlock_irqrestore(fifo->lock, flags);
- return ret;
- }
- #endif
复制代码- /*
- * A simple kernel FIFO implementation.
- *
- * Copyright (C) 2004 Stelian Pop <stelian@popies.net>
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- *
- */
- #include <linux/kernel.h>
- #include <linux/module.h>
- #include <linux/slab.h>
- #include <linux/err.h>
- #include <linux/kfifo.h>
- #include <linux/log2.h>
- /**
- * kfifo_init - allocates a new FIFO using a preallocated buffer
- * @buffer: the preallocated buffer to be used.
- * @size: the size of the internal buffer, this have to be a power of 2.
- * @gfp_mask: get_free_pages mask, passed to kmalloc()
- * @lock: the lock to be used to protect the fifo buffer
- *
- * Do NOT pass the kfifo to kfifo_free() after use! Simply free the
- * &struct kfifo with kfree().
- */
- struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size,
- gfp_t gfp_mask, spinlock_t *lock)
- {
- struct kfifo *fifo;
- /* size must be a power of 2 */
- BUG_ON(!is_power_of_2(size));
- fifo = kmalloc(sizeof(struct kfifo), gfp_mask);
- if (!fifo)
- return ERR_PTR(-ENOMEM);
- fifo->buffer = buffer;
- fifo->size = size;
- fifo->in = fifo->out = 0;
- fifo->lock = lock;
- return fifo;
- }
- EXPORT_SYMBOL(kfifo_init);
- /**
- * kfifo_alloc - allocates a new FIFO and its internal buffer
- * @size: the size of the internal buffer to be allocated.
- * @gfp_mask: get_free_pages mask, passed to kmalloc()
- * @lock: the lock to be used to protect the fifo buffer
- *
- * The size will be rounded-up to a power of 2.
- */
- struct kfifo *kfifo_alloc(unsigned int size, gfp_t gfp_mask, spinlock_t *lock)
- {
- unsigned char *buffer;
- struct kfifo *ret;
- /*
- * round up to the next power of 2, since our 'let the indices
- * wrap' technique works only in this case.
- */
- if (!is_power_of_2(size)) {
- BUG_ON(size > 0x80000000);
- size = roundup_pow_of_two(size);
- }
- buffer = kmalloc(size, gfp_mask);
- if (!buffer)
- return ERR_PTR(-ENOMEM);
- ret = kfifo_init(buffer, size, gfp_mask, lock);
- if (IS_ERR(ret))
- kfree(buffer);
- return ret;
- }
- EXPORT_SYMBOL(kfifo_alloc);
- /**
- * kfifo_free - frees the FIFO
- * @fifo: the fifo to be freed.
- */
- void kfifo_free(struct kfifo *fifo)
- {
- kfree(fifo->buffer);
- kfree(fifo);
- }
- EXPORT_SYMBOL(kfifo_free);
- /**
- * __kfifo_put - puts some data into the FIFO, no locking version
- * @fifo: the fifo to be used.
- * @buffer: the data to be added.
- * @len: the length of the data to be added.
- *
- * This function copies at most @len bytes from the @buffer into
- * the FIFO depending on the free space, and returns the number of
- * bytes copied.
- *
- * Note that with only one concurrent reader and one concurrent
- * writer, you don't need extra locking to use these functions.
- */
- unsigned int __kfifo_put(struct kfifo *fifo,
- const unsigned char *buffer, unsigned int len)
- {
- unsigned int l;
- len = min(len, fifo->size - fifo->in + fifo->out);
- /*
- * Ensure that we sample the fifo->out index -before- we
- * start putting bytes into the kfifo.
- */
- smp_mb();
- /* first put the data starting from fifo->in to buffer end */
- l = min(len, fifo->size - (fifo->in & (fifo->size - 1)));
- memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l);
- /* then put the rest (if any) at the beginning of the buffer */
- memcpy(fifo->buffer, buffer + l, len - l);
- /*
- * Ensure that we add the bytes to the kfifo -before-
- * we update the fifo->in index.
- */
- smp_wmb();
- fifo->in += len;
- return len;
- }
- EXPORT_SYMBOL(__kfifo_put);
- /**
- * __kfifo_get - gets some data from the FIFO, no locking version
- * @fifo: the fifo to be used.
- * @buffer: where the data must be copied.
- * @len: the size of the destination buffer.
- *
- * This function copies at most @len bytes from the FIFO into the
- * @buffer and returns the number of copied bytes.
- *
- * Note that with only one concurrent reader and one concurrent
- * writer, you don't need extra locking to use these functions.
- */
- unsigned int __kfifo_get(struct kfifo *fifo,
- unsigned char *buffer, unsigned int len)
- {
- unsigned int l;
- len = min(len, fifo->in - fifo->out);
- /*
- * Ensure that we sample the fifo->in index -before- we
- * start removing bytes from the kfifo.
- */
- smp_rmb();
- /* first get the data from fifo->out until the end of the buffer */
- l = min(len, fifo->size - (fifo->out & (fifo->size - 1)));
- memcpy(buffer, fifo->buffer + (fifo->out & (fifo->size - 1)), l);
- /* then get the rest (if any) from the beginning of the buffer */
- memcpy(buffer + l, fifo->buffer, len - l);
- /*
- * Ensure that we remove the bytes from the kfifo -before-
- * we update the fifo->out index.
- */
- smp_mb();
- fifo->out += len;
- return len;
- }
- EXPORT_SYMBOL(__kfifo_get);
复制代码 |
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