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Linux源码阅读笔记13-进程通信组件中

news 来源：原创 2024/9/20 4:31:12

架构图

代码分析

loff_t lnchannel_llseek(struct file *filp, loff_t offset, int whence) {loff_t newpos;switch(whence) {case 0:newpos = offset;break;case 1:newpos = filp->f_pos + offset;break;case 2:return -EINVAL;}if (newpos < 0 || newpos > LNCHANNEL_SIZE) {return -EINVAL;}filp->f_pos = newpos;return newpos;
}

这段代码是一个文件操作函数lnchannel_llseek()，它用于在文件中进行定位。具体来说，根据参数whenc e的值不同，函数将会根据指定的偏移量进行定位，并返回新的位置。

如果whence为0，则将偏移量直接作为新位置。
如果whence为1，则将当前位置(filp->f_pos)与偏移量相加得到新位置。
如果whence为2，则返回无效参数错误(EINVAL)。

在完成计算新位置之后，函数会对新位置进行合法性检查。如果新位置小于0或大于预定义的文件大小(LNCHANNEL_SIZE)，则会返回无效参数错误。

最后，函数更新文件结构体中的当前位置(filp->f_pos)为新位置，并返回新位置值。

unsigned int lnchannel_poll(struct file *filp, struct poll_table_struct *wait) {struct lnchannel* channel = filp->private_data;unsigned int mask = 0;poll_wait(filp, &channel->inq, wait);if (have_data) {mask |= (POLLIN | POLLRDNORM);}return mask;
}

这段代码是一个文件操作函数lnchannel_poll()，用于进行文件的轮询操作。它主要用于检查是否有数据可读，并返回相应的事件掩码。

首先，函数从文件结构体中获取通道指针channel。

接下来，使用poll_wait()函数将当前进程加入到等待队列中，以便在有新数据到达时唤醒进程。

然后，在判断是否有数据可读之前，代码中缺少了一个变量have_data的定义和赋值过程。在此处假设该变量为布尔类型，并且已经被正确初始化。

如果存在可读数据，则将事件掩码的对应位(POLLIN | POLLRDNORM)设置为1，表示可读事件发生。

最后，函数返回事件掩码mask给调用者，表示当前的文件状态。

需要注意的是，这只是代码片段，并没有提供完整的上下文环境。如果需要更详细的解释或有其他问题，请随时提问。

完整代码实现

#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <linux/io.h>
#include <linux/uaccess.h>
#include <linux/slab.h>
#include <linux/poll.h>#ifndef LNCHANNEL_MAJOR
#define LNCHANNEL_MAJOR     96
#endif#ifndef LNCHANNEL_NR_DEVS
#define LNCHANNEL_NR_DEVS   2
#endif#ifndef LNCHANNEL_SIZE
#define LNCHANNEL_SIZE      4096
#endif#define ENABLE_POLL     1struct lnchannel {char* data;unsigned long size;
#if ENABLE_POLLwait_queue_head_t inq;
#endif
};static int channel_major = LNCHANNEL_MAJOR;
module_param(channel_major, int, S_IRUGO);struct lnchannel* channel_devp;
struct cdev cdev;char have_data = 0;loff_t lnchannel_llseek(struct file *filp, loff_t offset, int whence) {loff_t newpos;switch(whence) {case 0:newpos = offset;break;case 1:newpos = filp->f_pos + offset;break;case 2:return -EINVAL;}if (newpos < 0 || newpos > LNCHANNEL_SIZE) {return -EINVAL;}filp->f_pos = newpos;return newpos;
}ssize_t lnchannel_read(struct file *filp, char __user *buffer, size_t size, loff_t *ppos) {int ret = 0;unsigned long count = size;unsigned long long p = *ppos;struct lnchannel* channel = filp->private_data;if (p >= LNCHANNEL_SIZE) {return 0;}if (count > LNCHANNEL_SIZE - p) {count = LNCHANNEL_SIZE - p;}while(!have_data) {if (filp->f_flags & O_NONBLOCK) {return -EAGAIN;}wait_event_interruptible(channel->inq, have_data);}if (copy_to_user(buffer, (void*)(channel->data + p), count)) {ret = -EFAULT;}else {ret = strlen(buffer);channel->size -= ret;printk(KERN_INFO "read %d btye(s) from %ld\n", ret, p);}have_data = 0;return ret;
}ssize_t lnchannel_write(struct file *filp, const char __user *buffer, size_t size, loff_t * ppos) {int ret = 0;unsigned long count = size;unsigned long long p = *ppos;struct lnchannel* channel = filp->private_data;if (p >= LNCHANNEL_SIZE) {return ret;}if (count >= LNCHANNEL_SIZE - p) {count = LNCHANNEL_SIZE - p;}if (copy_from_user(channel->data + p, buffer, count)) {return -EFAULT;}else {*(channel->data + p + count) = '\0';channel->size += count;ret = count;*ppos += count;printk(KERN_INFO, "written %d btyes from %ld\n", count, p);}have_data = 1;wake_up(channel->inq);return ret;
}int lnchannel_mmap(struct file *filp, struct vm_area_struct *vma) {vma->vm_flags |= VM_IO;vma->vm_flags |= (VM_DONTEXPAND | VM_DONTDUMP);if (remap_pfn_range(vma, vma->vm_start, virt_to_phys(channel->data) >> PAGE_SHIFT, vma->vm_end-vma->vm_start, vma->vm_page_prot)) {return -EAGAIN;}return 0;
}int lnchannel_open(struct inode *inode, struct file *filp) {struct lnchannel* channel;int num = MINOR(inode->i_cdev);if (num >= LNCHANNEL_NR_DEVS) {return -ENODEV;}channel = &channel_devp[num];filp->private_data = channel;return 0;}int lnchannel_release(struct inode *, struct file *) {return 0;
}unsigned int lnchannel_poll(struct file *filp, struct poll_table_struct *wait) {struct lnchannel* channel = filp->private_data;unsigned int mask = 0;poll_wait(filp, &channel->inq, wait);if (have_data) {mask |= (POLLIN | POLLRDNORM);}return mask;
}static const struct file_operations lnchannel_fops = {.owner = THIS_MODULE,.llseek = lnchannel_llseek,.open = lnchannel_open,.write = lnchannel_write,.open = lnchannel_open,.release = lnchannel_release,.mmap = lnchannel_mmap,.poll = lnchannel_poll,
};static int lnchannel_init(void) {int result;int i;dev_t devno = MKDEV(channel_major, 0);if (channel_major) {result = register_chrdev_region(devno, LNCHANNEL_NR_DEVS, "lnchannel");}else {result = alloc_chrdev_region(&devno, 0, LNCHANNEL_NR_DEVS, "lnchannel");channel_major = MAJOR(devno);}if (result < 0) return result;cdev_init(&cdev, &lnchannel_fops);cdev.owner = THIS_MODULE;cdev_add(&cdev, MKDEV(channel_major, 0), LNCHANNEL_NR_DEVS);channel_devp = kmalloc(LNCHANNEL_NR_DEVS * (struct lnchannel), GFP_KERNEL);if (!channel_devp) {result = -ENOMEM;goto fail_malloc;}memset(channel_devp, 0, sizeof(struct lnchannel));for(i = 0; i < LNCHANNEL_NR_DEVS; i++) {channel_devp[i].size = LNCHANNEL_SIZE;channel_devp[i].data = kmalloc(LNCHANNEL_SIZE, GFP_KERNEL);memset(channel_devp[i].data, 0, LNCHANNEL_SIZE);init_waitqueue_head(&(channel_devp[i].inq));}printk(KERN_INFO "linchannel_init");return 0;fail_malloc:unregister_chrdev_region(devno, 1);return result;
}static void lnchannel_exit(void) {printk(KERN_INFO "lnchannel_exit");cdev_del(&cdev);kfree(channel_devp);unregister_chrdev_region(MKDEV(channel_major, 0), 2);
}MODULE_AUTHOR("Lenn Louis");
MODULE_LICENSE("GPL");module_init(lnchannel_init);
module_init(lnchannel_exit);

#!/bin/bashccflags_y += -O2ifneq ($(KERNELRELEASE),)
obj-m := lnchannel.o
else
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)default:$(MAKE) -C $(KERNELDIR) M=$(PWD) modules 
endifclean:rm -rf *.o *.ko *.mod.cdepend .depend dep:$(CC)  -M *.c > .depend