linux-kernel - Re: [PATCH v2 6/9] debugfs: Implement debugfs_create

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Date:   Sat, 27 Mar 2021 11:41:36 +0100
From:   Greg KH <greg@...ah.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>, mingo@...nel.org,
        mgorman@...e.de, juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        bristot@...hat.com, joshdon@...gle.com, valentin.schneider@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/9] debugfs: Implement debugfs_create_str()

On Fri, Mar 26, 2021 at 04:19:12PM +0100, Peter Zijlstra wrote:
> On Fri, Mar 26, 2021 at 03:58:37PM +0100, Rasmus Villemoes wrote:
> > >   kmalloc(len + 2, ...);
> > 
> > No, because nul-terminating the stuff you pass to
> > simple_read_from_buffer is pointless cargo-culting. Yeah, read_file_bool
> > does it, but that's just bogus.
> 
> Urgh, feel yuck to not have it zero terminated, but if you feel strongly
> about it I suppose I can make it go away.
> 
> > > 	len = strscpy(copy, str, len);
> > > 	if (len < 0)
> > > 		return len;
> > 
> > To what end? The only way that could possibly return -EFOO is if the
> > nul-terminator in str vanished between the strlen() and here, and in
> > that case you have bigger problems.
> 
> There are strings in the kernel which we rewrite in most ugly ways,
> task_struct::comm comes to mind. Best be paranoid.
> 
> > > Copy-pasta from debugfs_*_bool(). This thing seems to export everything
> > > and I figured I'd go along with that.
> > 
> > I thought the convention was not to export anything until the kernel
> > itself had a (modular) user.
> 
> That's generally how I feel too. But this really isn't my subsystem so I
> more or less try to mimmick what I see done there.

I'll take some time next week and go through and remove any exports in
debugfs that are not actually needed for exports as it's been a while
since I last looked...

But that should not affect this change, it's fine to me as-is.

thanks,

greg k-h