请给出响应用户mremap系统调用的内核内核驱动程序实例

下面是一个响应mremap系统调用的内核驱动程序示例：

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/version.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("mremap driver");

static int my_mremap(struct file *filep, struct vm_area_struct *vma,
                     unsigned long old_addr, unsigned long old_size,
                     unsigned long new_addr, unsigned long new_size)
{
    int ret = 0;
    struct page *page = NULL;

    if (new_size > old_size) {
        // Expand memory mapping
        unsigned long npages = (new_size - old_size) >> PAGE_SHIFT;
        while (npages-- > 0) {
            page = alloc_page(GFP_KERNEL);
            if (!page) {
                printk(KERN_ERR "Failed to allocate page\n");
                ret = -ENOMEM;
                goto out;
            }

            ret = vm_insert_page(vma, new_addr + old_size, page);
            if (ret < 0) {
                printk(KERN_ERR "Failed to insert page\n");
                __free_page(page);
                goto out;
            }

            old_size += PAGE_SIZE;
        }
    } else if (new_size < old_size) {
        // Shrink memory mapping
        unsigned long npages = (old_size - new_size) >> PAGE_SHIFT;
        while (npages-- > 0) {
            page = vmalloc_to_page((void *) new_addr + new_size);
            if (!page) {
                printk(KERN_ERR "Failed to get page\n");
                ret = -EFAULT;
                goto out;
            }

            ret = vm_delete_page(vma, new_addr + new_size, page);
            if (ret < 0) {
                printk(KERN_ERR "Failed to delete page\n");
                goto out;
            }

            __free_page(page);
            old_size -= PAGE_SIZE;
        }
    }

    // Update memory mapping
    vma->vm_end = new_addr + new_size;
    vma->vm_pgoff = new_addr >> PAGE_SHIFT;

out:
    return ret;
}

static const struct file_operations fops = {
    .mremap = my_mremap,
};

static int __init mremap_init(void)
{
    int ret = 0;

    ret = register_chrdev(0, "mremap", &fops);
    if (ret < 0) {
        printk(KERN_ERR "Failed to register device\n");
        goto out;
    }

    printk(KERN_INFO "mremap driver loaded\n");

out:
    return ret;
}

static void __exit mremap_exit(void)
{
    unregister_chrdev(0, "mremap");

    printk(KERN_INFO "mremap driver unloaded\n");
}

module_init(mremap_init);
module_exit(mremap_exit);

以上代码中，我们定义了一个my_mremap()函数来处理mremap系统调用。在这个函数中，我们首先检查新的映射大小是否比旧的映射大小大，如果是，则分配新的页面，并将它们插入到内存映射区域中。如果新的映射大小比旧的映射大小小，则删除不再需要的页面。

最后，我们更新内存映射区域的大小和页偏移，并返回适当的错误代码。我们将这个函数作为file_operations结构体的mremap字段的值，以便内核可以调用它来处理mremap系统调用。