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 1 struct lnchannel { char* data; unsigned long size; #if ENABLE_POLL wait_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/bash ccflags_y += -O2 ifneq ($(KERNELRELEASE),) obj-m := lnchannel.o else KERNELDIR ?= /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) default: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules endif clean: rm -rf *.o *.ko *.mod.c depend .depend dep: $(CC) -M *.c > .depend
