写一段sd卡的驱动程序

这里是一个简单的SD卡驱动程序（适用于Linux内核）：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/hdreg.h>
#include <linux/genhd.h>
#include <linux/bio.h>

#define SD_CARD_MAJOR 240

static int sd_card_size = 1024 * 1024 * 16;   // SD卡大小为16MB
static struct gendisk *sd_card_disk;
static struct request_queue *sd_card_queue;

static int sd_card_open(struct block_device *bdev, fmode_t mode)
{
    printk(KERN_INFO "SD Card: device opened\n");
    return 0;
}

static void sd_card_release(struct gendisk *gd, fmode_t mode)
{
    printk(KERN_INFO "SD Card: device closed\n");
}

static struct block_device_operations sd_card_ops = {
    .owner = THIS_MODULE,
    .open = sd_card_open,
    .release = sd_card_release,
};

static void sd_card_request(struct request_queue *q)
{
    struct bio *bio;

    while ((bio = blk_fetch_request(q)) != NULL) {
        if (bio->bi_sector >= get_capacity(sd_card_disk)) {
            printk(KERN_ERR "SD Card: bad request: block=%llu, count=%u\n",
                (unsigned long long)bio->bi_sector, bio->bi_size / 512);
            bio_endio(bio, -EIO);
            continue;
        }

        switch (bio_rw(bio)) {
        case READ:
            printk(KERN_INFO "SD Card: read %u sectors from %llu\n",
                bio->bi_size / 512, (unsigned long long)bio->bi_sector);
            break;
        case WRITE:
            printk(KERN_INFO "SD Card: write %u sectors to %llu\n",
                bio->bi_size / 512, (unsigned long long)bio->bi_sector);
            break;
        default:
            printk(KERN_ERR "SD Card: unknown operation %u\n", bio_rw(bio));
            bio_endio(bio, -EIO);
            continue;
        }

        bio_endio(bio, 0);
    }
}

static int __init sd_card_init(void)
{
    int err;

    sd_card_disk = alloc_disk(1);
    if (!sd_card_disk) {
        printk(KERN_ERR "SD Card: failed to allocate disk\n");
        return -ENOMEM;
    }

    sd_card_disk->major = SD_CARD_MAJOR;
    sd_card_disk->first_minor = 0;
    sd_card_disk->fops = &sd_card_ops;
    sd_card_disk->queue = sd_card_queue = blk_init_queue(sd_card_request, NULL);
    sd_card_disk->private_data = NULL;
    sprintf(sd_card_disk->disk_name, "sd_card");
    set_capacity(sd_card_disk, sd_card_size / 512);
    add_disk(sd_card_disk);

    printk(KERN_INFO "SD Card: driver initialized\n");
    return 0;

err_free_queue:
    blk_cleanup_queue(sd_card_queue);
err_free_disk:
    put_disk(sd_card_disk);
    return err;
}

static void __exit sd_card_exit(void)
{
    del_gendisk(sd_card_disk);
    put_disk(sd_card_disk);
    blk_cleanup_queue(sd_card_queue);

    printk(KERN_INFO "SD Card: driver unloaded\n");
}

module_init(sd_card_init);
module_exit(sd_card_exit);
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("SD Card driver");

该驱动程序创建了一个SD卡设备，并提供了读写操作。在初始化时，它将SD卡分配给一个gendisk结构体，并设置请求队列的回调函数。在请求函数中，它获取并处理读写请求。

请注意，这只是一个简单的示例，实际的SD卡驱动程序需要处理更多细节和错误情况。