linux-kernel - Re: [PATCH] vc_screen: break from vcs_read() while loop if vcs

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Message-ID: <Y+FHd2WR9w6zBZd7@kroah.com>
Date:   Mon, 6 Feb 2023 19:31:19 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     George Kennedy <george.kennedy@...cle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>, jslaby@...e.cz,
        sfr@...b.auug.org.au, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH] vc_screen: break from vcs_read() while loop if vcs_vc()
 returns NULL

On Mon, Feb 06, 2023 at 01:20:28PM -0500, George Kennedy wrote:
> 
> 
> On 2/6/2023 1:12 PM, Linus Torvalds wrote:
> > On Mon, Feb 6, 2023 at 9:34 AM George Kennedy <george.kennedy@...cle.com> wrote:
> > > 
> > > -               ret = -ENXIO;
> > >                  vc = vcs_vc(inode, &viewed);
> > > -               if (!vc)
> > > +               if (!vc) {
> > > +                       if (read)
> > > +                               break;
> > > +                       ret = -ENXIO;
> > >                          goto unlock_out;
> > > +               }
> > That works, but the whole "if (read)" thing is already done after the
> > loop, so instead of essentially duplicating that logic, I really think
> > the patch should be just a plain
> > 
> >                  vc = vcs_vc(inode, &viewed);
> >                  if (!vc)
> > -                       goto unlock_out;
> > +                       break;
> > 
> > and nothing else.
> > 
> > And yes, the pre-existing vcs_size() error handling has that same ugly pattern.
> > 
> > It might be worth cleaning up too, although right now that
> > 
> >                  size = vcs_size(vc, attr, uni_mode);
> >                  if (size < 0) {
> >                          if (read)
> >                                  break;
> > 
> > pattern means that if we 'break' there, 'read' is non-zero, so 'ret'
> > doesn't matter. Which is also ugly, but works.
> > 
> > I *think* it could all be rewritten to just use 'break' everywhere in
> > the loop, and make 'ret' handling be saner.
> > 
> > Something like the attached patch, but while I tried to think about
> > it, I didn't spend a lot of effort on it, and I certainly didn't test
> > it. So I'm sending this out as a "Hmm. This _looks_ better to me, but
> > whatever" patch.
> 
> Thank you Linus,
> 
> Will start with your suggested patch and will test it.

And I'll go drop your patch from my tree before the 0-day bots pick it
up :)

thanks,

greg k-h