linux-kernel - Re: [char-misc-next v2 1/5] mei: set parent for char device

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Message-ID: <2025071623-lasso-twenty-9b9a@gregkh>
Date: Wed, 16 Jul 2025 09:47:20 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: "Usyskin, Alexander" <alexander.usyskin@...el.com>
Cc: "Abliyev, Reuven" <reuven.abliyev@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [char-misc-next v2 1/5] mei: set parent for char device

On Wed, Jul 16, 2025 at 07:44:28AM +0000, Usyskin, Alexander wrote:
> > Subject: Re: [char-misc-next v2 1/5] mei: set parent for char device
> > 
> > On Mon, Jun 30, 2025 at 01:02:12PM +0000, Usyskin, Alexander wrote:
> > > > Subject: Re: [char-misc-next v2 1/5] mei: set parent for char device
> > > >
> > > > On Mon, Jun 30, 2025 at 12:19:38PM +0300, Alexander Usyskin wrote:
> > > > > Connect char device to parent device to avoid
> > > > > parent device unload while char device is
> > > > > still held open by user-space.
> > > >
> > > > No, that's not what cdev_set_parent() does.
> > > >
> > > https://elixir.bootlin.com/linux/v6.16-rc3/source/fs/char_dev.c#L511
> > > * cdev_set_parent() sets a parent kobject which will be referenced
> > >  * appropriately so the parent is not freed before the cdev. This
> > >  * should be called before cdev_add.
> > >
> > > This is what written there. Is my interpretation wrong?
> > 
> > It has nothing to do with a char device being open or closed from
> > userspace, it has to deal with properly placing the device in the
> > kobject tree and the object references being correct.
> > 
> > Surely the mei device had this set up before, right?  If not, how did
> > sysfs look with these char devices with no real parent?
> > 
> 
> Mei device never had this setup.

So what is the "parent" of a mei device today?

> I've looked at other drivers - some of them do not have this setup.

Then they are broken, don't copy them :)

thanks,

greg k-h