【嵌入式Linux】基于kernel6.1的块设备驱动（RAM Disk），示例代码和测试
1.驱动结构梳理
驱动使用BIO+BLK_MQ框架，BIO负责我们的具体驱动代码，BLK_MQ负责分发处理BIO请求（BLK_MQ是为了应对：1.多核心分发；2.合并相邻的块请求；3.满足调度需求）。
其他具体的见大佬文章：linux驱动移植-linux块设备驱动blk-mq - 大奥特曼打小怪兽 - 博客园
2.源码结构zzl_ramdisk.c
2.1.头文件
2.2.宏定义
2.3.定义、声明和变量
2.4.open打开设备回调
2.5.release关闭设备回调
2.6.getgeo获取设备物理信息回调
heads是磁头数量（和盘片数量一般是对应关系）
cylinders代表一个盘片上磁道数量（有多少圈）
sectors代表一个磁道，有多少扇区（硬盘电路会处理，让软件上看上去，所有磁道扇区数量一样）
2.7.fops装载2.4、2.5、2.6回调
用于传入给上层虚文件系统（VFS）调用
2.8.dev_handle_request，BLK_MQ请求处理回调
轮询处理队列中的IO请求，读取的话，从设备中拷贝
2.9.ramdisk_mq_ops装载2.8回调
2.10.demo_init驱动初始化（加载）
2.10.1.申请私人对象（我们自定义的对象）结构体的变量
2.10.2.申请vfs的buffer（RAM Disk中的RAM）
2.10.3.申请设备号
2.10.4.申请并初始化BLK_MQ的目标信息（回调、队列信息、节点选择）
2.10.5.使用目标信息和私人对象，申请并初始化磁盘设备对象gendisk
2.10.6.设置request_queue的扇区字节数参数
2.10.7.添加磁盘设备
2.11.demo_exit驱动卸载
释放内存、删除设备
3.源码
#include <linux/module.h> #include <linux/init.h> #include <linux/kernel.h> #include <linux/fs.h> // 包含 file_operations 结构体 #include <linux/uaccess.h> // 包含 copy_to_user, copy_from_user #include <linux/slab.h> // 包含 kzalloc, kfree #include <linux/blkdev.h> #include <linux/device.h> #include <linux/hdreg.h> #include <linux/blkdev.h> #include <linux/blk-mq.h> // #include <linux/genhd.h> #include <linux/vmalloc.h> #include <linux/spinlock.h> #define DEVICE_NAME "ZZL_RAMDISK" #define RAMDISK_SIZE (16*1024*1024) // 16MiB #define RAMDISK_SECTOR_SIZE (512) #define RAMDISK_SECTOR_NUM (RAMDISK_SIZE/RAMDISK_SECTOR_SIZE) /* 设备私有数据：指向模拟内存的指针 */ struct ramdisk_dev { unsigned char *buffer; }; static struct gendisk *ramdisk_gendisk; static struct ramdisk_dev *ramdisk_priv; static int ramdisk_major; static struct blk_mq_tag_set ramdisk_tag_set; static int dev_open(struct block_device *bdev, fmode_t mode) { printk(KERN_INFO "设备打开\n"); return 0; } static void dev_release(struct gendisk *disk, fmode_t mode) { printk(KERN_INFO "设备关闭\n"); } static int dev_getgeo(struct block_device *bdev, struct hd_geometry *geo) { geo->heads = 4; geo->cylinders = 32; geo->sectors = RAMDISK_SECTOR_NUM/(geo->heads * geo->cylinders); return 0; } static const struct block_device_operations fops = { .owner = THIS_MODULE, .open = dev_open, .getgeo = dev_getgeo, .release = dev_release, }; static blk_status_t dev_handle_request(struct blk_mq_hw_ctx *hctx, const struct blk_mq_queue_data *bd) { struct request *req = bd->rq; struct ramdisk_dev *dev = req->q->queuedata; struct bio *bio; struct bio_vec bvec; struct bvec_iter iter; unsigned long offset; size_t len; void *src, *dst; if (!dev || !dev->buffer) { printk(KERN_ALERT "私有数据或缓冲区无效\n"); return BLK_STS_IOERR; } for (bio = req->bio; bio; bio = bio->bi_next) { offset = bio->bi_iter.bi_sector << SECTOR_SHIFT; if (offset+len >= RAMDISK_SIZE) { pr_alert("bio 起始偏移越界: %lu\n", offset); return BLK_STS_IOERR; } bio_for_each_segment(bvec, bio, iter) { len = bvec.bv_len; if (bio_data_dir(bio) == READ) { src = dev->buffer + offset; dst = kmap_local_page(bvec.bv_page) + bvec.bv_offset; memcpy(dst, src, len); kunmap_local(dst); printk(KERN_INFO "读取 %zu - %zu\n", offset, offset+len); } else { src = kmap_local_page(bvec.bv_page) + bvec.bv_offset; dst = dev->buffer + offset; memcpy(dst, src, len); kunmap_local(src); printk(KERN_INFO "写入 %zu - %zu\n", offset, offset+len); } offset += len; } } blk_mq_end_request(req, BLK_STS_OK); return BLK_STS_OK; } static const struct blk_mq_ops ramdisk_mq_ops = { .queue_rq = dev_handle_request, }; static int __init demo_init(void) { int ret = 0; // 1. ramdisk_priv = kzalloc(sizeof(*ramdisk_priv), GFP_KERNEL); if(IS_ERR(ramdisk_priv )) { printk(KERN_ALERT "申请Prive失败\n"); return PTR_ERR(ramdisk_priv ); } printk(KERN_INFO "申请Prive 成功\n"); ramdisk_priv->buffer = vmalloc(RAMDISK_SIZE); if(IS_ERR(ramdisk_priv->buffer)) { printk(KERN_ALERT "申请Buffer失败\n"); kfree(ramdisk_priv); return PTR_ERR(ramdisk_priv->buffer); } memset(ramdisk_priv->buffer, 0, RAMDISK_SIZE); printk(KERN_INFO "申请Buffer 成功\n"); // 2. ramdisk_major = register_blkdev(0, DEVICE_NAME); if(ramdisk_major < 0) { printk(KERN_ALERT "分配驱动号失败\n"); vfree(ramdisk_priv->buffer); kfree(ramdisk_priv); return ramdisk_major; } printk(KERN_INFO "驱动号：%d\n", ramdisk_major); // . memset(&ramdisk_tag_set, 0, sizeof(ramdisk_tag_set)); ramdisk_tag_set.ops = &ramdisk_mq_ops; ramdisk_tag_set.nr_hw_queues = 1; ramdisk_tag_set.queue_depth = 128; // 队列深度 ramdisk_tag_set.numa_node = NUMA_NO_NODE; ramdisk_tag_set.flags = BLK_MQ_F_SHOULD_MERGE; ramdisk_tag_set.cmd_size = 0; ret = blk_mq_alloc_tag_set(&ramdisk_tag_set); if (ret) { printk(KERN_ALERT "分配 tag_set 失败\n"); unregister_blkdev(ramdisk_major, DEVICE_NAME); vfree(ramdisk_priv->buffer); kfree(ramdisk_priv); return ret; } // 3. ramdisk_gendisk = blk_mq_alloc_disk(&ramdisk_tag_set, ramdisk_priv); if (IS_ERR(ramdisk_gendisk)) { // 错误处理，注销设备号 printk(KERN_ALERT "申请GenDisk失败\n"); vfree(ramdisk_priv->buffer); kfree(ramdisk_priv); unregister_blkdev(ramdisk_major, DEVICE_NAME); blk_mq_free_tag_set(&ramdisk_tag_set); return PTR_ERR(ramdisk_gendisk); } printk(KERN_INFO "申请GenDisk 成功\n"); // 3.1. ramdisk_gendisk->major = ramdisk_major; ramdisk_gendisk->first_minor = 0; ramdisk_gendisk->minors = 1; strcpy(ramdisk_gendisk->disk_name, DEVICE_NAME); ramdisk_gendisk->fops = &fops; set_capacity(ramdisk_gendisk, RAMDISK_SECTOR_NUM); // 3.2. struct request_queue *req_q = ramdisk_gendisk->queue; blk_queue_logical_block_size(req_q, RAMDISK_SECTOR_SIZE); blk_queue_physical_block_size(req_q, RAMDISK_SECTOR_SIZE); // 4. ret = add_disk(ramdisk_gendisk); if(ret) { printk(KERN_ALERT "添加Disk失败\n"); vfree(ramdisk_priv->buffer); kfree(ramdisk_priv); unregister_blkdev(ramdisk_major, DEVICE_NAME); blk_mq_free_tag_set(&ramdisk_tag_set); return ret; } printk(KERN_INFO "驱动完成注册\n"); return ret; } static void __exit demo_exit(void) { del_gendisk(ramdisk_gendisk); put_disk(ramdisk_gendisk); unregister_blkdev(ramdisk_major, DEVICE_NAME); vfree(ramdisk_priv->buffer); kfree(ramdisk_priv); blk_mq_free_tag_set(&ramdisk_tag_set); printk(KERN_INFO "驱动卸载\n"); } module_init(demo_init); module_exit(demo_exit); MODULE_AUTHOR("[ZZL]"); MODULE_DESCRIPTION("Testing block (Ram Disk) driver"); MODULE_LICENSE("GPL v2");4.Makefile
obj-m += zzl_ramdisk.o all: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules clean: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean5.测试步骤
5.1.编译安装驱动
编译为.ko文件，然后用insmod安装.ko文件
make sudo insmod zzl_ramdisk.ko5.2.创建文件夹、挂载设备
sudo mkdir -p /mnt/ramdisk sudo mount /dev/ZZL_RAMDISK /mnt/ramdisk5.3.创建文件，查看磁盘状态
echo "Hello RAM Disk" | sudo tee /mnt/ramdisk/test.txt dd if=/dev/urandom of=/mnt/ramdisk/random_file.bin bs=8M count=1 status=progress ls -l /mnt/ramdisk/ df -h