Re: [RFC PATCH v1 3/4] ml-lib: Implement simple testing character device driver

["greg@kroah.com" <greg@kroah.com>]

On Mon, Feb 09, 2026 at 08:56:47PM +0000, Viacheslav Dubeyko wrote:
> On Sat, 2026-02-07 at 16:55 +0100, Greg KH wrote:
> > On Fri, Feb 06, 2026 at 11:11:35AM -0800, Viacheslav Dubeyko wrote:
> > > Implement simple testing character device driver
> > > 
> > > Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
> > 
> > It's hard to tell if this is just an early april-fools joke or not, but
> > if it's not:
> > 
> > > +### Character Device Operations
> > > +- **Open/Close**: Device can be opened and closed multiple times
> > > +- **Read**: Read data from a kernel buffer
> > > +- **Write**: Write data to a kernel buffer (1KB capacity)
> > > +- **Seek**: Support for lseek() operations
> > > +
> > > +### IOCTL Commands
> > > +- `ML_LIB_TEST_DEV_IOCRESET`: Clear the device buffer
> > > +- `ML_LIB_TEST_DEV_IOCGETSIZE`: Get current data size
> > > +- `ML_LIB_TEST_DEV_IOCSETSIZE`: Set data size
> > > +
> > > +### Sysfs Attributes
> > > +Located at `/sys/class/ml_lib_test/mllibdev`:
> > > +- `buffer_size`: Maximum buffer capacity (read-only)
> > > +- `data_size`: Current amount of data in buffer (read-only)
> > > +- `access_count`: Number of times device has been opened (read-only)
> > > +- `stats`: Comprehensive statistics (opens, reads, writes)
> > 
> > Again, this is not an acceptable use of sysfs.
> 
> Maybe, I am missing your point. Are you assuming that I am going to share huge
> pieces of data by means of sysfs? If so, then I am not going to use sysfs for
> it.

Please do not use sysfs for this at all.

> > > +	/* Allocate device number */
> > > +	ret = alloc_chrdev_region(&dev_number, 0, 1, DEVICE_NAME);
> > 
> > Don't burn a cdev for this, please use the misc device api.
> > 
> 
> It is not real-life driver. It is only testing driver with the goal to
> check/test the ML library infrastructure and to show the potential way of using
> the ML library.
> 
> As the next step, I am planning to use the ML library for two potential real-
> life use-case: (1) GC subsystem of LFS file system, (2) ML-based DAMON approach.
> 
> So, this driver is only testing engine of implementing and testing the vision of
> ML library.

We don't take code that uses apis incorrectly. Please do not use a cdev
for this type of "testing" driver, that is the incorrect thing to do and
actually makes your code more complex than it needs to.

good luck!

greg k-h