linux-kernel - Re: [PATCH v3 1/8] tty: n_gsm: add restart parameter to DLC specific ioctl config

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Date:   Mon, 24 Apr 2023 16:20:00 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     "Starke, Daniel" <daniel.starke@...mens.com>
cc:     "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v3 1/8] tty: n_gsm: add restart parameter to DLC specific
 ioctl config

On Mon, 24 Apr 2023, Greg KH wrote:

> On Mon, Apr 24, 2023 at 11:03:26AM +0000, Starke, Daniel wrote:
> > > > --- a/include/uapi/linux/gsmmux.h
> > > > +++ b/include/uapi/linux/gsmmux.h
> > > > @@ -58,7 +58,8 @@ struct gsm_dlci_config {
> > > >  	__u32 priority;		/* Priority (0 for default value) */
> > > >  	__u32 i;		/* Frame type (1 = UIH, 2 = UI) */
> > > >  	__u32 k;		/* Window size (0 for default value) */
> > > > -	__u32 reserved[8];	/* For future use, must be initialized to zero */
> > > > +	__u32 restart;		/* Force DLCI channel reset? */
> > > 
> > > Why are you using a full 32 bits for just 1 bit of data here?  Why not
> > > use a bitfield?
> > 
> > The ioctrl guide states:
> >   Bitfields and enums generally work as one would expect them to,
> >   but some properties of them are implementation-defined, so it is better
> >   to avoid them completely in ioctl interfaces.
> > 
> > Therefore, I tried to avoid them here.
> 
> Then use a u8?

To add further, I think that the ioctl guidance tries to say that C 
bitfields using :number postfix are not a good idea, not that much to 
disallow flag like content within an integer type.

-- 
 i.

> > > And what happened to the request to turn the documentation for this
> > > structure into proper kerneldoc format?
> > 
> > That applied to patch 2/8 and is unrelated to this patch. Another patch
> > will need to fix this.
> > 
> > Link: https://lore.kernel.org/all/20230424075251.5216-2-daniel.starke@siemens.com/
> 
> It's kind of related in that the format is not right :)
> 
> As it's a few weeks before I am allowed to even apply this, please
> rework the series a bit.
> 
> thanks,
> 
> greg k-h
>