79 lines
1.7 KiB
C
79 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/miscdevice.h>
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#include <linux/fs.h>
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#include <linux/slab.h>
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Louis Solofrizzo <louis@ne02ptzero.me>");
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MODULE_DESCRIPTION("Useless module");
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static ssize_t myfd_read(struct file *fp, char __user *user,
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size_t size, loff_t *offs);
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static ssize_t myfd_write(struct file *fp, const char __user *user,
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size_t size, loff_t *offs);
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static const struct file_operations myfd_fops = {
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.owner = THIS_MODULE,
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.read = &myfd_read,
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.write = &myfd_write
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};
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static struct miscdevice myfd_device = {
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.minor = MISC_DYNAMIC_MINOR,
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.name = "reverse",
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.fops = &myfd_fops
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};
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char str[PAGE_SIZE];
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DEFINE_MUTEX(rw_lock); //lock read/write operations of the /dev/reverse file
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static int __init myfd_init(void)
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{
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mutex_init(&rw_lock);
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return misc_register(&myfd_device);
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}
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static void __exit myfd_cleanup(void)
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{
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misc_deregister(&myfd_device);
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}
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ssize_t myfd_read(struct file *fp, char __user *user, size_t size, loff_t *offs)
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{
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ssize_t retval;
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size_t len;
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char *tmp;
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mutex_lock(&rw_lock);
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len = strlen(str);
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tmp = kmalloc(sizeof(char) * PAGE_SIZE, GFP_KERNEL);
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for (size_t i = 0, j = len - 1; i < len; i++, j--)
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tmp[i] = str[j];
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tmp[len] = 0;
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retval = simple_read_from_buffer(user, size, offs, tmp, len);
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mutex_unlock(&rw_lock);
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kfree(tmp);
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return retval;
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}
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ssize_t myfd_write(struct file *fp, const char __user *user, size_t size,
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loff_t *offs)
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{
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ssize_t res;
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if (size >= (PAGE_SIZE - 1))
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return -EINVAL;
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mutex_lock(&rw_lock);
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res = simple_write_to_buffer(str, size, offs, user, size);
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str[res] = 0x0;
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mutex_unlock(&rw_lock);
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return res;
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}
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module_init(myfd_init);
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module_exit(myfd_cleanup);
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