linux-kernel - Re: [PATCH v2 2/5] sysctl: Add flags to support min/max range clamping

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Date:   Wed, 28 Feb 2018 19:06:01 +0000
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v2 2/5] sysctl: Add flags to support min/max range
 clamping

On Wed, Feb 28, 2018 at 01:58:53PM -0500, Waiman Long wrote:
> On 02/28/2018 01:43 PM, Luis R. Rodriguez wrote:
> > On Wed, Feb 28, 2018 at 12:53:40PM -0500, Waiman Long wrote:
> >> On 02/27/2018 07:47 PM, Luis R. Rodriguez wrote:
> >>> On Tue, Feb 27, 2018 at 03:49:48PM -0500, Waiman Long wrote:
> >>>> When minimum/maximum values are specified for a sysctl parameter in
> >>>> the ctl_table structure with proc_dointvec_minmax() handler,
> >>> an
> >>>
> >>>> update
> >>>> to that parameter will fail with error if the given value is outside
> >>>> of the required range.
> >>>>
> >>>> There are use cases where it may be better to clamp the value of
> >>>> the sysctl parameter to the given range without failing the update,
> >>>> especially if the users are not aware of the actual range limits.
> >>> Makes me wonder if we should add something which does let one query
> >>> for the ranges. Then scripts can fetch that as well.
> >> That will actually be better than printing out the range in the dmesg
> >> log. However, I haven't figured out an easy way of doing that. If you
> >> have any suggestion, please let me know about it.
> > I think a macro that also adds yet another proc read-only entry with a postfix
> > "_range" with an internal handler which prints the range may suffice.
> >
> >   Luis
> 
> I think that is a possible solution. Instead of adding a macro, I will
> add one more flag which does the magic when the ctl_table entry is being
> processed. I think that will be simpler from the user point of view.

Agreed, flag should work nicely too. And likely easier to read / review
and maintain.

  Luis