mirror of
https://github.com/cirosantilli/linux-kernel-module-cheat.git
synced 2026-01-13 20:12:26 +00:00
139 lines
3.3 KiB
C
139 lines
3.3 KiB
C
/* https://cirosantilli.com/linux-kernel-module-cheat#file-operations */
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#include <linux/debugfs.h>
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#include <linux/errno.h> /* EFAULT */
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#include <linux/fs.h> /* file_operations */
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#include <linux/kernel.h> /* min */
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#include <linux/module.h>
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#include <linux/printk.h> /* printk */
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#include <linux/uaccess.h> /* copy_from_user, copy_to_user */
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#include <uapi/linux/stat.h> /* S_IRUSR */
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static struct dentry *debugfs_file;
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static char data[] = {'a', 'b', 'c', 'd'};
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static int open(struct inode *inode, struct file *filp)
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{
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pr_info("open\n");
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return 0;
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}
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/* @param[in,out] off: gives the initial position into the buffer.
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* We must increment this by the ammount of bytes read.
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* Then when userland reads the same file descriptor again,
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* we start from that point instead.
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*/
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static ssize_t read(struct file *filp, char __user *buf, size_t len, loff_t *off)
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{
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ssize_t ret;
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pr_info("read\n");
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pr_info("len = %zu\n", len);
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pr_info("off = %lld\n", (long long)*off);
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if (sizeof(data) <= *off) {
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ret = 0;
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} else {
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ret = min(len, sizeof(data) - (size_t)*off);
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if (copy_to_user(buf, data + *off, ret)) {
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ret = -EFAULT;
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} else {
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*off += ret;
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}
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}
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pr_info("buf = %.*s\n", (int)len, buf);
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pr_info("ret = %lld\n", (long long)ret);
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return ret;
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}
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/* Similar to read, but with one notable difference:
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* we must return ENOSPC if the user tries to write more
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* than the size of our buffer. Otherwise, Bash > just
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* keeps trying to write to it infinitely.
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*/
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static ssize_t write(struct file *filp, const char __user *buf, size_t len, loff_t *off)
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{
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ssize_t ret;
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pr_info("write\n");
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pr_info("len = %zu\n", len);
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pr_info("off = %lld\n", (long long)*off);
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if (sizeof(data) <= *off) {
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ret = 0;
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} else {
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if (sizeof(data) - (size_t)*off < len) {
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ret = -ENOSPC;
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} else {
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if (copy_from_user(data + *off, buf, len)) {
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ret = -EFAULT;
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} else {
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ret = len;
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pr_info("buf = %.*s\n", (int)len, data + *off);
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*off += ret;
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}
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}
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}
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pr_info("ret = %lld\n", (long long)ret);
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return ret;
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}
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/* Called on the last close:
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* http://stackoverflow.com/questions/11393674/why-is-the-close-function-is-called-release-in-struct-file-operations-in-the-l
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*/
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static int release(struct inode *inode, struct file *filp)
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{
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pr_info("release\n");
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return 0;
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}
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static loff_t llseek(struct file *filp, loff_t off, int whence)
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{
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loff_t newpos;
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pr_info("llseek\n");
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pr_info("off = %lld\n", (long long)off);
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pr_info("whence = %lld\n", (long long)whence);
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switch(whence) {
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case SEEK_SET:
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newpos = off;
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break;
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case SEEK_CUR:
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newpos = filp->f_pos + off;
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break;
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case SEEK_END:
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newpos = sizeof(data) + off;
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break;
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default:
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return -EINVAL;
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}
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if (newpos < 0) return -EINVAL;
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filp->f_pos = newpos;
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pr_info("newpos = %lld\n", (long long)newpos);
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return newpos;
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}
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static const struct file_operations fops = {
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/* Prevents rmmod while fops are running.
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* Try removing this for poll, which waits a lot. */
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.owner = THIS_MODULE,
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.llseek = llseek,
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.open = open,
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.read = read,
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.release = release,
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.write = write,
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};
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static int myinit(void)
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{
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debugfs_file = debugfs_create_file("lkmc_fops", S_IRUSR | S_IWUSR, NULL, NULL, &fops);
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return 0;
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}
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static void myexit(void)
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{
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debugfs_remove_recursive(debugfs_file);
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}
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module_init(myinit)
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module_exit(myexit)
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MODULE_LICENSE("GPL");
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