linux-kernel - Re: [tip: perf/core] perf/core: Convert snprintf() to scnprintf()

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Date:   Wed, 21 Sep 2022 14:55:35 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Jules Irenge <jbi.octave@...il.com>, x86@...nel.org
Subject: Re: [tip: perf/core] perf/core: Convert snprintf() to scnprintf()

On Wed, Sep 21, 2022 at 12:44:35PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Wed, Sep 21, 2022 at 08:08:55AM -0000, tip-bot2 for Jules Irenge wrote:
> > > The following commit has been merged into the perf/core branch of tip:
> > > 
> > > Commit-ID:     678739d622ae7b75b62d550858b6bf104c43e2df
> > > Gitweb:        https://git.kernel.org/tip/678739d622ae7b75b62d550858b6bf104c43e2df
> > > Author:        Jules Irenge <jbi.octave@...il.com>
> > > AuthorDate:    Sun, 18 Sep 2022 00:41:08 +01:00
> > > Committer:     Ingo Molnar <mingo@...nel.org>
> > > CommitterDate: Wed, 21 Sep 2022 10:01:20 +02:00
> > > 
> > > perf/core: Convert snprintf() to scnprintf()
> > > 
> > > Coccinelle reports a warning:
> > > 
> > >     WARNING: use scnprintf or sprintf
> > > 
> > > Adding to that, there has also been some slow migration from snprintf to scnprintf.
> > > 
> > > This LWN article explains the rationale for this change:
> > > 
> > >     https: //lwn.net/Articles/69419/
> > > 
> > > No change in behavior.
> > > 
> > > [ mingo: Improved the changelog. ]
> > 
> > And yet, at this point I still have no clue what's wrong with
> > snprintf(). So not much improvement :/
> 
> I've added this to the changelog:
> 
>     perf/core: Convert snprintf() to scnprintf()

I'm not sure if it would apply in this case as it's for a device
attribute, but there's another helper sysfs_emit that does the safe
print to string and one does not have to care which flavor of s*printf
it is. We had patches in btrfs converting from snprintf to scnprintf and
the latest one is sysfs_emit which is convenient to use but assumes the
PAGE_SIZE of the buffer.