Re: [RFC] QR encoding for Oops messages

[Levente Kurusa <levex@linux.com>]

Hi,

On 03/22/2014 07:20 PM, Teodora Băluţă wrote:
> On Sat, Mar 22, 2014 at 7:09 PM, Levente Kurusa <levex@linux.com> wrote:
>> Hi,
>>
>> On 03/21/2014 02:28 PM, Jason Cooper wrote:
>>> On Wed, Mar 19, 2014 at 10:38:30PM +0200, Teodora Băluţă wrote:
>>>> On Wed, Mar 19, 2014 at 10:18 PM, Dave Jones <davej@redhat.com> wrote:
>>>>> On Mon, Mar 17, 2014 at 02:59:47PM -0700, Teodora Baluta wrote:
>>>>>  > This feature encodes Oops messages into a QR barcode that is scannable by
>>>>>  > any device with a camera.
>>>>>
>>>>> [...]
>>>>>
>>>>> That's a ton of code we're adding into one of the most fragile parts of the kernel.
>>>>>
>>>>> A lot of what libqrencode does would seem to be superfluous to the requirements
>>>>> here, as we don't output kernel oopses in kanji for eg, and won't care about
>>>>> multiple versions of the qr spec.
>>>>
>>>> That's true. I didn't do that much cleanup in the library afraid of
>>>> breaking something and focused that I get this done one way or
>>>> another. Indeed, the library is userspace and is made to be versatile
>>>> rather than small.
>>>
>>> Perhaps you could add libqr to the staging tree?  As long as it
>>> compiles, it can go there.  Then you can focus on cleanups and bloat
>>> removal.  In the process, you'll get a larger testing base because it
>>> will be in mainline.
>>
>> Yea that is a better way. However, the current state of the code has
>> several problems:
>>
>> * No good error handling (simply returns -1 on failure no matter what)
>>    I have began converting this to the ERR_PTR et al interface
>>    However, I have not yet done this fully due to the vast amount
>>    of work required to do so.
>>    This shouldn't be yet merged, but I shall send it as patches once
>>    it gets into the staging tree.
>>
>> * All memory allocations are GFP_ATOMIC for no reason.
>>    I have converted them to GFP_KERNEL since we can block safely.
>>    This could be merged to Teodora's branch. I can send her a pull
>>    request on GitHub if she wants so.
> 
> Since we are talking about some kernel Oopses I thought that making
> this GFP_ATOMIC ensures that we get memory allocation. I have
> considered using GFP_KERNEL, but I am not very sure about that.
> Probably somewhere deep inside I wanted to make it work even for
> panics. :(

Yea that makes sense, realized that just after I sent the mail.
However, since this is in lib/ other parts might want to be
able to use it and for them GFP_KERNEL makes more sense.

> 
>>
>> * Selecting QR_OOPS and QRLIB currently does not build due to
>>    undefined references to zlib_deflate* functions.
>>    This is due to QRLIB not selecting ZLIB_DEFLATE.
>>    Fixed this as well. Can be merged to Teodora if she wants.
> 
> Hmm, that's odd. I thought I added a 'depends' in the menu. Please
> make a pull request and I'll merge it immediately.

Sent it, also attached the patch [0].

> 
>>
>> * I had trouble getting QR output.
>>    Doing 'echo c > /proc/sysrq-trigger' triggered a crash,
>>    but it resulted in a recursive OOPS. This is a nullptr-deref
>>    and hence I think it may be related to the fact I was running
>>    it in textmode. :-)
>>    Or, it is due to the bugged error handling.
> 
> The QR output is written to the frame buffer. That means you have to
> get acces to a console. As I mentioned in the RFC, I am looking for an
> alternative to using fb.h since that doesn't seem to work very well
> atm.

Yea this issue is significant. There are some ASCII codes which might
work in textmode though. (219-223) Maybe it's worth a shot to try it out.

> 
>>
>>>
>>> You may be interested in objdiff [1] which I'm using for merging code
>>> into the staging tree [2].  It provides an automated way to determine
>>> that code cleanups didn't change the resultant object code.  You can see
>>> an example run here [3].
> 
> I'll take a look. Thanks!
> 
>>>
>>> I would definitely like to see the QR output incorporated into a
>>> kernel.org url.  That would remove the need for installing another app,
>>> and would ease bug reporting.
>>
>> I still struggle to understand how could that be done. We can encode the
>> QR code as ASCII. Okay, that's fine, however it is very long. Encoding
>> 'Unable to handle kernel paging request at 0000000f' gave a 449 character
>> long sequence with very strange characters [0]. We should try to shorten
>> it, imho. Not sure how to do that though.
>>
>> oops.kernel.org/?qr=CODE  would look cool though. :-)
> 
> I am not very sure that could be done. Accessing the QR code through a
> link would mean you have to send it automatically to kernel.org (that
> assumes a great deal of things like working Internet connection) and
> it misses the point of having a QR code in the first place. The way I
> see it, having a QR decoder app installed that can do an offline
> decoding is a less greater effort than popping out a browser on the
> machine you're working on.

Yea I still think that mobiles are the way to go. However, why would we
need internet connection? We could just output a formatted link like
oops.kernel.org/?qr=%s

where %s will take the ASCII QR Code. Or something among those lines.

> 
> And plus, as Levente said, encoding the QR code which does the Oops
> message encoding as text again (which would be large) would generate a
> very large link.

Yes, if we could solve this it could work very nicely.



[0]:

----------------%<----------------------
From: Levente Kurusa <levex@linux.com>
Subject: [PATCH] qr: fix missing dependency

ZLIB_DEFLATE is required by QRLIB. Select it.

Signed-off-by: Levente Kurusa <levex@linux.com>
---
 lib/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Kconfig b/lib/Kconfig
index ef591d6..3743907 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -437,6 +437,7 @@ config SIGNATURE

 config QRLIB
 	bool "QR encoding library"
+	select ZLIB_DEFLATE
 	help
 	  QR encoding library

-- 
1.8.3.1


-- 
Regards,
Levente Kurusa