一、篇头

继续使用qemu调试内核的实验。

二、系列文章

略……

三、实验环境

• 编译服务器+NFS：ubuntu 22.04
• Qemu 虚拟机：Linux version 5.15.102 + Buysbox 1.3.36 + ARM_32bit

Qemu 启动命令：qemu-system-arm -nographic -M vexpress-a9 -m 1024M -kernel arch/arm/boot/zImage -initrd …/busybox/rootfs.ext4.img.gz -dtb arch/arm/boot/dts/vexpress-v2p-ca9.dtb

四、源码

4.1 KFIFO介绍

Linux内核实现了一个称为KFIFO的环形缓冲区的机制，它可以在一个读者线程和一个写者线程并发执行的场景下，无须使用额外的加锁来保证环形缓冲区的数据安全。同时由此机制来管理了缓冲区的使用情况，省去许多是，特别方便。

KFIFO提供的接口函数定义在include/linux/kfifo.h文件中。

4.1.1 声明及定义：DEFINE_KFIFO(fifo, type, size)

/*** DEFINE_KFIFO - macro to define and initialize a fifo* @fifo: name of the declared fifo datatype* @type: type of the fifo elements* @size: the number of elements in the fifo, this must be a power of 2** Note: the macro can be used for global and local fifo data type variables.*/
#define DEFINE_KFIFO(fifo, type, size) \DECLARE_KFIFO(fifo, type, size) = \(typeof(fifo)) { \{ \{ \.in	= 0, \.out	= 0, \.mask	= __is_kfifo_ptr(&(fifo)) ? \0 : \ARRAY_SIZE((fifo).buf) - 1, \.esize	= sizeof(*(fifo).buf), \.data	= __is_kfifo_ptr(&(fifo)) ? \NULL : \(fifo).buf, \} \} \}

4.1.2 用户写：kfifo_from_user(fifo, from, len, copied)

/*** kfifo_from_user - puts some data from user space into the fifo* @fifo: address of the fifo to be used* @from: pointer to the data to be added* @len: the length of the data to be added* @copied: pointer to output variable to store the number of copied bytes** This macro copies at most @len bytes from the @from into the* fifo, depending of the available space and returns -EFAULT/0.** Note that with only one concurrent reader and one concurrent* writer, you don't need extra locking to use these macro.*/
#define	kfifo_from_user(fifo, from, len, copied) \
__kfifo_uint_must_check_helper( \
({ \typeof((fifo) + 1) __tmp = (fifo); \const void __user *__from = (from); \unsigned int __len = (len); \unsigned int *__copied = (copied); \const size_t __recsize = sizeof(*__tmp->rectype); \struct __kfifo *__kfifo = &__tmp->kfifo; \(__recsize) ? \__kfifo_from_user_r(__kfifo, __from, __len,  __copied, __recsize) : \__kfifo_from_user(__kfifo, __from, __len, __copied); \
}) \
)

4.1.3 用户读：kfifo_to_user(fifo, to, len, copied)

/*** kfifo_to_user - copies data from the fifo into user space* @fifo: address of the fifo to be used* @to: where the data must be copied* @len: the size of the destination buffer* @copied: pointer to output variable to store the number of copied bytes** This macro copies at most @len bytes from the fifo into the* @to buffer and returns -EFAULT/0.** Note that with only one concurrent reader and one concurrent* writer, you don't need extra locking to use these macro.*/
#define	kfifo_to_user(fifo, to, len, copied) \
__kfifo_int_must_check_helper( \
({ \typeof((fifo) + 1) __tmp = (fifo); \void __user *__to = (to); \unsigned int __len = (len); \unsigned int *__copied = (copied); \const size_t __recsize = sizeof(*__tmp->rectype); \struct __kfifo *__kfifo = &__tmp->kfifo; \(__recsize) ? \__kfifo_to_user_r(__kfifo, __to, __len, __copied, __recsize) : \__kfifo_to_user(__kfifo, __to, __len, __copied); \
}) \
)

4.2 驱动源码

• 文件名：linux-stable\my_kmodules\test_5.c

#include 
#include 
#include 
#include 
#include 
#include #define MY_DEV_NAME "my_dev"DEFINE_KFIFO(my_kfifo, char, 128);
static char kbuf[128];static int test_5_open(struct inode *inode, struct file *file)
{int major = MAJOR(inode->i_rdev);int minor = MINOR(inode->i_rdev);pr_info("%s: major=%d, minor=%d\n", __func__, major, minor);return 0;
}static int test_5_release(struct inode *inode, struct file *file)
{pr_info("%s \n", __func__);return 0;
}static ssize_t test_5_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{int ret;unsigned int copied_count=0;pr_info("%s \n", __func__);ret = kfifo_to_user(&my_kfifo, buf,  count, &copied_count);if(ret != 0) {return -EIO;}pr_info("%s ：%s, count=%d, copied_count=%d\n", __func__, my_kfifo.buf,  count, copied_count);return copied_count;
}static ssize_t test_5_write(struct file *file, const char __user *buf, size_t count, loff_t *f_pos)
{int ret;unsigned int copied_count=0;pr_info("%s \n", __func__);ret = kfifo_from_user(&my_kfifo, buf, count, &copied_count);if(ret != 0) {return -EIO;}pr_info("%s , my_kfifo.buf=%s\n", __func__, my_kfifo.buf);//注意：使用用户空间的buf，需要先copy_from_userret = copy_from_user(kbuf, buf, copied_count);pr_info("%s ：%s, count=%d, copied_count=%d, ret=%d\n", __func__, kbuf,  count, copied_count, ret);return copied_count;
}static const struct file_operations test_fops = {.owner = THIS_MODULE,.open = test_5_open,.release = test_5_release,.read = test_5_read,.write = test_5_write
};static struct miscdevice test_5_misc_device ={.minor = MISC_DYNAMIC_MINOR,.name = MY_DEV_NAME,.fops = &test_fops,
};static int __init test_5_init(void)
{int ret;pr_info("test_5_init\n");ret = misc_register(&test_5_misc_device);if (ret != 0 ) {pr_err("failed to misc_register");return ret;}pr_err("Minor number = %d\n", test_5_misc_device.minor);return 0;
}static void __exit test_5_exit(void)
{pr_info("test_5_exit\n");misc_deregister(&test_5_misc_device);
}module_init(test_5_init);
module_exit(test_5_exit);MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("szhou <66176468@qq.com>");
MODULE_DESCRIPTION("test_5, 使用misc、KFIFO开发设备驱动");

4.3 APP源码

本次实验，直接使用 echo /cat 负责设备的写/读。

4.4 Makefile

• 文件名：linux-stable\my_kmodules\Makefile

KDIR := /home/szhou/works/qemu_linux/linux-stableobj-m := test_1.o test_2.o test_3.o test_4.o  test_5.o
all :$(MAKE) -C $(KDIR) M=$(PWD) modules
clean:$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) cleanrm -f *.ko

五、编译及部署

（1）执行驱动KO编译
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ make 
make -C /home/szhou/works/qemu_linux/linux-stable M=/home/szhou/works/qemu_linux/linux-stable/my_kmodules modules
make[1]: Entering directory '/home/szhou/works/qemu_linux/linux-stable'CC [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_5.oMODPOST /home/szhou/works/qemu_linux/linux-stable/my_kmodules/Module.symversLD [M]  /home/szhou/works/qemu_linux/linux-stable/my_kmodules/test_5.ko
make[1]: Leaving directory '/home/szhou/works/qemu_linux/linux-stable'
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ cp test_5.ko ~/works/nfs_share/
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ （2）将KO和APP存放到NFS共享目录
szhou@bc01:~/works/qemu_linux/linux-stable/my_kmodules$ cp test_5.ko ~/works/nfs_share/

六、运行及测试

（1）启动之前编译组建的QEMU虚拟机
----------------------------------------
Welcome to szhou's tiny Linux
----------------------------------------Please press Enter to activate this console. （2）挂载NFS共享目录
~ #  mount -t nfs -o nolock 192.168.3.67:/home/szhou/works/nfs_share /mnt（3） 加载ko
~ # cd /mnt/
/mnt # insmod test_5.ko 
test_5: loading out-of-tree module taints kernel.
test_5_init
Minor number = 125
/mnt # 
/mnt # mdev  -s
/mnt # （4）写入字符串 
/mnt # echo "hellow kfifo" >  /dev/my_dev 
test_5_open: major=10, minor=125
test_5_write 
test_5_write , my_kfifo.buf=hellow kfifotest_5_write ：hellow kfifo
, count=13, copied_count=13, ret=0
test_5_release 
/mnt # （5）读取字符串 
/mnt # cat /dev/my_dev 
test_5_open: major=10, minor=125
test_5_read 
test_5_read ：hellow kfifo
, count=4096, copied_count=13
hellow kfifo
test_5_read 
test_5_read ：hellow kfifo
, count=4096, copied_count=0
test_5_release 
/mnt # 

操作画面如下图：