writing data to debugfs --- from a device driver - linux-kernel

Question

With proc we can easily use read & write system call as shown in this example.
write on /proc entry through user space
But i am working on passing information from driver to user-space using debugfs.
I am able to find these two example code. Here application is able to read and write to debugfs file using mmap() system call.
http://people.ee.ethz.ch/~arkeller/linux/code/mmap_simple_kernel.c
http://people.ee.ethz.ch/~arkeller/linux/code/mmap_user.c
But suppose in my case requirement for communicating using Debugfs file with device driver:
user-space application <-------> debugfs file <-------> Device driver
So can i use same code mmap_simple_kernel.c inside my --->> device driver code --->> and transfer data to debugfs directly from driver ? But in this case there will be two file_operations structures inside my driver will it cause some problem ? Is it right approach ?
Or just like application is following process in -- mmap_user.c --- same process -- i follow in my device driver program. And keep mmap_simple_kernel.c as seprate module for debugfs entry ?

Answer 1

You can take a look at how kmemleak uses debugfs in mm/kmemleak.c:
static const struct seq_operations kmemleak_seq_ops = {
.start = kmemleak_seq_start,
.next = kmemleak_seq_next,
.stop = kmemleak_seq_stop,
.show = kmemleak_seq_show,
};
static int kmemleak_open(struct inode *inode, struct file *file)
{
return seq_open(file, &kmemleak_seq_ops);
}
static int kmemleak_release(struct inode *inode, struct file *file)
{
return seq_release(inode, file);
}
static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
size_t size, loff_t *ppos)
{...}
static const struct file_operations kmemleak_fops = {
.owner = THIS_MODULE,
.open = kmemleak_open,
.read = seq_read,
.write = kmemleak_write,
.llseek = seq_lseek,
.release = kmemleak_release,
};
dentry = debugfs_create_file("kmemleak", S_IRUGO, NULL, NULL,
&kmemleak_fops);

Answer 2

This question is the top search result in Google for mmap debugfs. I am adding here an important information. According to this https://lkml.org/lkml/2016/5/21/73 post debugfs_create_file() in the kernel 4.8.0 or higher will ignore .mmap field in the struct file_operations
Use debugfs_create_file_unsafe() as a workaround