linux-kernel - Re: [PATCH 1/2] Staging: comedi: comedi_fops: Change comedi_num_legacy

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Date:   Wed, 8 Mar 2017 17:38:12 +0800
From:   Cheah Kok Cheong <thrust73@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     abbotti@....co.uk, hsweeten@...ionengravers.com,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] Staging: comedi: comedi_fops: Change
 comedi_num_legacy_minors type

Dear Greg,
  Thanks for taking the time to review.

On Tue, Mar 07, 2017 at 08:01:38PM +0100, Greg KH wrote:
> On Sun, Mar 05, 2017 at 03:22:32AM +0800, Cheah Kok Cheong wrote:
> > Change to unsigned to allow removal of negative value check in
> > init section.
> 
> Why?
> 

User can input a -ve number as parameter for module loading.
This will be caught by the mentioned check and cause loading to fail.
I think the original intention here is to inform user via kernel log
the acceptable input range.

Now if a user doesn't know how to access the log, it's of no help.

If a user does know how to access the log, probably also know how
to use modinfo or know that reserving a -ve number of minors is
not acceptable.

IMHO, this check is pointless and best enforced in module_param.

> > Use smaller data type since the max possible value currently is 48.
> 
> Does it matter?
> 

You are right it doesn't matter and not worth the effort doing unless
concurrent work is being done in this area.
Which is what patch 2/2 is trying to do here.
Please note that I've sent V2. Patch 1/2 unchanged and 2/2 with amended
commit log.

Thanks,
Brgds,
CheahKC

> thanks,
> 
> greg k-h