内核并发竞态解决机制

#include <linux/init.h>#include <linux/module.h>#include <linux/kernel.h>#include <linux/version.h>#include <asm/io.h>#include <linux/fs.h>#include <linux/cdev.h>#include <linux/slab.h>#include <asm/uaccess.h> #include <linux/highmem.h> #include <asm/kmap_types.h>MODULE_LICENSE("Dual BSD/GPL");MODULE_DESCRIPTION("a simple driver example!");struct fifo{dev_t num;struct cdev cdev;//int available;atomic_t available;//struct mutex lock;//spinlock_t lock;//queue propertychar *qbuf;int start; //posint end;   //posint cursize;int maxsize;}FIFO;static int fifo_open(struct inode *inodep, struct file *filep){//printk("fifo open called\n");//local_irq_disable();//mutex_lock(&FIFO.lock);//spin_lock(&FIFO.lock);//if(FIFO.available)//{//FIFO.available = 0;//local_irq_enable();//mutex_unlock(&FIFO.lock);//spin_unlock(&FIFO.lock);if(0 == atomic_dec_and_test(&FIFO.available))return 0;//}//local_irq_enable();//mutex_unlock(&FIFO.lock);//spin_unlock(&FIFO.lock);atomic_inc(&FIFO.available, 1);return -EBUSY;}static ssize_t fifo_read (struct file *f, char __user *p, size_t n, loff_t *off){int size = n>FIFO.cursize?FIFO.cursize:n;if(size == 0)return 0;int len1, len2;if(FIFO.start <= FIFO.end)// copy once{if(copy_to_user(p, FIFO.qbuf, size)){printk("copy to user fail1\n");return -EINVAL;}}else{len1 = FIFO.maxsize-FIFO.start;if(copy_to_user(p, &FIFO.qbuf[FIFO.start], len1)){printk("copy to user fail2\n");return -EINVAL;}len2 = size-len1;if(copy_to_user(p+len1, FIFO.qbuf, len2)){printk("copy to user fail3\n");return -EINVAL;}}FIFO.start = (FIFO.start+size)%FIFO.maxsize;FIFO.cursize -= size;return size;}static ssize_t fifo_write (struct file *f, const char __user *p, size_t n, loff_t *off){int space = FIFO.maxsize - FIFO.cursize;int size = n>space?space:n;int len1 = (FIFO.maxsize-1 - FIFO.end);int len2;if(!space)return 0;//copy_from_user(&FIFO.qbuf[end+1], p, size);if(len1 >= size)//copy once{if(copy_from_user(&FIFO.qbuf[FIFO.end+1], p, size)){printk("copy from user fail1\n");return -EINVAL;}}else{if(copy_from_user(&FIFO.qbuf[FIFO.end+1], p, len1)){printk("copy from user fail2\n");return -EINVAL;}len2 = size-len1;if(copy_from_user(FIFO.qbuf, p+len1,  len2)){printk("copy from user fail3\n");return -EINVAL;}}FIFO.end = (FIFO.end+size)%FIFO.maxsize;FIFO.cursize += size;return size;}static long fifo_ioctl(struct file *f, unsigned int cmd, unsigned long arg){return 0;}static int fifo_release(struct inode *inodep, struct file *filep){//printk("fifo closed\n");//FIFO.available = 1;atomic_inc(&FIFO.available, 1);return 0;}int fifo_mmap(struct file *f, struct vm_area_struct *vma){return remap_pfn_range(vma, vma->vm_start, virt_to_phys(FIFO.qbuf)>>PAGE_SHIFT, vma->vm_end-vma->vm_start, vma->vm_page_prot);}struct file_operations myops = {.owner = THIS_MODULE,.open = fifo_open,.unlocked_ioctl  = fifo_ioctl,.read = fifo_read,.write = fifo_write,.mmap = fifo_mmap,.release = fifo_release};static int __init mymodule_init(void){int ret = 0;printk("fifo module in\n");//FIFO.available = 1;atomic_init(&FIFO.available, 1);//mutex_init(&FIFO.lock);//spin_lock_init(&FIFO.lock);FIFO.qbuf = (char*)__get_free_page(GFP_KERNEL);FIFO.maxsize = 1<<PAGE_SHIFT;FIFO.cursize = FIFO.start = 0;FIFO.end = -1;//request dev numret = alloc_chrdev_region(&FIFO.num, 0, 1, "fifodddddddddd");if(ret){printk("devnum alloc fail!\n");return ret;}printk("num: %d\n", MAJOR(FIFO.num) );//create cdev object#if 0FIFO.mycdev =  cdev_alloc();if(NULL==fifo.mycdev){printk("alloc cdev fail!\n");goto cdev_alloc_out;}#endif//init cdev opscdev_init(&FIFO.cdev,  &myops);FIFO.cdev.owner = THIS_MODULE;//register cdev into kernelret = cdev_add(&FIFO.cdev, FIFO.num, 1);if(ret){printk("add cdev fail!\n");goto cdev_add_out;}return 0;cdev_add_out:#if 0kfree(FIFO.mycdev);#endif//cdev_alloc_out:unregister_chrdev_region(FIFO.num, 1);return ret;}static void __exit mymodule_exit(void){//unregister cdev from kernelcdev_del(&FIFO.cdev);#if 0//release cdev objectkfree(&FIFO.cdev);#endif//release dev numunregister_chrdev_region(FIFO.num, 1); free_page((unsigned long)FIFO.qbuf);printk("fifo module release\n");}module_init(mymodule_init);module_exit(mymodule_exit);

总结：

1. 屏蔽本地中断

2. 互斥锁

3. 信号量

4. 自旋锁

5. 原子操作