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Date:   Tue, 12 Feb 2019 16:20:53 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     cgxu519 <cgxu519@gmx.com>
Cc:     viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH 2/2] chardev: showing minor range for chardev in the
 output of /proc/devices
Message-ID: <20190212152053.GA25804@kroah.com>
References: <20190212084739.27602-1-cgxu519@gmx.com>
 <20190212084739.27602-2-cgxu519@gmx.com>
 <20190212090212.GE31657@kroah.com>
 <a8332299-818e-571c-efc9-7885f18eddb8@gmx.com>
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On Tue, Feb 12, 2019 at 11:18:22PM +0800, cgxu519 wrote:
> On 2/12/19 5:02 PM, Greg KH wrote:
> > On Tue, Feb 12, 2019 at 04:47:39PM +0800, Chengguang Xu wrote:
> > > Currently chardev allows to share major, showing
> > > major with minor range for chardev will be more
> > > helpful.
> > > 
> > > Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
> > > ---
> > >   fs/char_dev.c | 4 +++-
> > >   1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/char_dev.c b/fs/char_dev.c
> > > index b25b1da097d5..6f00acdeb308 100644
> > > --- a/fs/char_dev.c
> > > +++ b/fs/char_dev.c
> > > @@ -55,7 +55,9 @@ void chrdev_show(struct seq_file *f, off_t offset)
> > >   	mutex_lock(&chrdevs_lock);
> > >   	for (cd = chrdevs[major_to_index(offset)]; cd; cd = cd->next) {
> > >   		if (cd->major == offset)
> > > -			seq_printf(f, "%3d %s\n", cd->major, cd->name);
> > > +			seq_printf(f, "%3d %s (%u-%u)\n", cd->major, cd->name,
> > > +				   cd->baseminor,
> > > +				   cd->baseminor + cd->minorct - 1);
> > You are changing the format of a userspace file, what tools are going to
> > break when you do this?
> 
> I'll remove this part in V2. Do you have any idea how to get the minor
> range info for particular major? Or adding a similar file to somewhere
> under /sys is acceptable?

Why do you need to know the minor range?  What can userspace do with
this that actually matters?

thanks,

greg k-h