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

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Date:   Thu, 29 Sep 2022 09:28:04 +0100
From:   Jules Irenge <jbi.octave@...il.com>
To:     David Sterba <dsterba@...e.cz>
Cc:     peterz@...radead.org, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [tip: perf/core] perf/core: Convert snprintf() to scnprintf()

On Wed, Sep 21, 2022 at 02:55:35PM +0200, David Sterba wrote:
> 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.

Yes, you are right. I can resend the patch with sysfs_emit() if

possible as the latest documentation on sysfs states that 

show() device function should only use sysfs_emit() or sysfs_emit_at() 
when formatting the value to be returned to user space.

* https://www.kernel.org/doc/html/latest/filesystems/sysfs.html

I don't know whether it may apply to this subsystem.  I have to read
more about it and test

thanks
jules