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

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Message-ID: <2026020719-thrive-domain-f0c2@gregkh>
Date: Sat, 7 Feb 2026 16:55:14 +0100
From: Greg KH <greg@...ah.com>
To: Viacheslav Dubeyko <slava@...eyko.com>
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, bpf@...r.kernel.org,
	Slava.Dubeyko@....com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 3/4] ml-lib: Implement simple testing character
 device driver

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@...eyko.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.

> +	/* 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.

good luck!

greg k-h