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

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Date:   Mon, 6 Feb 2023 13:20:28 -0500
From:   George Kennedy <george.kennedy@...cle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     gregkh@...uxfoundation.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 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.

George
>
>                 Linus