Linux Developers Consider On-Screen QR Codes For Kernel Panics 175
An anonymous reader writes "Linux kernel developers are currently evaluating the possibility of using QR codes to display kernel oops/panic messages. Right now a lot of text is dumped to the screen when a kernel oops occurs, most of which isn't easily archivable by normal Linux end-users. With QR codes as Linux oops messages, a smart-phone could capture the display and either report the error string or redirect them to an error page on Kernel.org. The idea of using QR codes within the Linux kernel is still being discussed by upstream developers."
Good idea (Score:5, Insightful)
Huh? (Score:2, Insightful)
Re:Good idea (Score:2, Insightful)
how soon until someone accidentally posts a QR code containing confidential information, since they cannot read it themselves.
Re:Good idea (Score:5, Insightful)
Very unlikely.. the information in a QR code is probably just enough to say "I run kernel X (build Y) and it crashed with error code Z at instruction 12345 in module 123", if it was a kernel dump that's different but I have seen these without the QR codes and there's nothing sensitive there.
Wish other OSs did this... (Score:3, Insightful)
Anything's an improvement over:
"My computer froze."
"What happened?"
"It put some message on the screen."
"What did it say?"
"Something about an error."
"What error?"
"I dunno. It had some numbers and letters and stuff."
Re:Not enough data (Score:2, Insightful)
1) No, 2953 bytes is not enough for a "kernel dump". "Kernel dump" as a term/phrase doesn't even make any sense, come to think of it. Did you mean a stack trace? Register dump? Because "kernel dump" makes me think of "memory dump", i.e. dumping all contents of RAM to swap + rebooting system (which later notices the crash dump header in swap and hopefully extracts it).
2) If just a stack trace or register dump: 40-L may be too high a resolution to reliably work when using a mobile phone camera to take a picture of an LCD screen. There's often too much noise (high ISO) in this situation. Lower-resolution QR codes means more likely successful recognition and decoding. http://en.wikipedia.org/wiki/Image_noise#Low_and_high-ISO_noise_examples
3) What I haven't seen mentioned: how exactly do the developers plan on printing a QR code when someone's using a text-only console? Don't tell me "everything on Linux console uses a graphical framebuffer now" because that's completely false (lots of folks disable this, and some distros disable it by default). What's going to happen when the kernel crashes? It uses BIOS INT 0x10 to switch to 320x200 VGA mode and show a QR code? Is it going to change the on-screen font masks/bitmaps to display "tiled" pixel data that represents a QR code?
I have a better idea: how about just keeping things how they are. People using mobile phones to take a photo of a stack trace + register dump mostly works reliably (barring wobbly hands). Console fonts are quite legible even if the person has consumed too much cappuccino, while QR codes, especially high-resolution QR codes, are going to be a lot less legible in that situation. My reaction to this proposal would be: what does using a QR code get us that we don't already have available with existing technology and methodologies in place? (FYI: the correct answer to that question is: "nothing")
Re:Wish other OSs did this... (Score:5, Insightful)
And with QR codes, the conversation becomes this:
"My computer froze."
"What happened?"
"It put some white and black crap on the screen."
"What did it say?"
"How the fuck should I know? It was random white and black dots! Like a fucking Rorschach test!"
"It probably was a kernel panic. What was the error?"
"I dunno, because like I said, ALL IT HAD WAS SOME DOTS AND SHIT. Then it rebooted! So it's gone! FUCK!"
How is that an improvement? Yes it's a change, but it's not an improvement.
You get the prize of dumbest comment on slashdot (Score:2, Insightful)
Really? You think your end user who hasn't got the brains to take a screenshot of human readable text and send it to you and who probably has never even heard of QR codes is going to have the presence of mind and technical knowledge and ability to take a picture of the code and send it to you?
That has to be one of the dumbest things I've heard on slashdot...and that's REALLY saying something.
It's even more worrying that the Linux Kernel devs are giving this idea the time of day.
Re:Good idea (Score:3, Insightful)
Here's a crazy idea: instead of working on displaying cutesy graphics images that need to be decoded using a smart phone and a web site, what about actually generating a freakin' crash dump? Is there a technical reason that Linux is unable to do this? If crash dumps are really not possible, how about a plain 'ol text file in the root directory containing the reason for the crash/panic?
The matrix (Score:3, Insightful)
Re:Good idea (Score:5, Insightful)
Kernel crashes occur when the kernel enters an inconsistent or invalid state from which it cannot recover.
When a user program fails, the kernel maintains consistency, can cleanly terminate the process, and can accurately report the cause of the failure if need be (illegal instruction, deadlock, access violation, etc...).
When a kernel fails the very systems that it relies on to report failures may very well be compromised by whatever caused the kernel to fail in the first place. As such, any kernel fault reporting needs to be incredibly robust and as independent of other kernel mechanisms as possible. Dumping text to a serial terminal is the preferred method because it's incredibly simple and relies on nothing else, meaning that barring a failure of the system memory it should always act as a reliable fallback.
Dumping kernel memory to a disk might fail if the state of the file system is compromised, if the storage controller is compromised, or if any number of intermediary systems are compromised by the inconsistent state of the kernel. Many operating systems do attempt to dump crash memory to the swap file / swap partition as this is less likely to cause data corruption than writing to a particular file in the file system.
It "can" be done, but that does not necessarily make it a good idea.
Re:Wish other OSs did this... (Score:3, Insightful)
I doubt the kernel developer that implements this would forget to put the message
"Make a photo of this black-and-white dots and send it to crash@kernel.org so we can try to figure out what happened. Thanks for making the Linux kernel better!"
at the top of the black and white dots.
Re:Good idea (Score:4, Insightful)
You usually don't want to write to the filesystem in the event of a kernel panic. It could make things worse and corrupt it. Once you kernel panic you are basically screwed and can't rely on any services beyond really low level BIOS stuff to work. Poking some text to the screen buffer is about it.
Windows does core dumps using a specially reserved area of the boot drive and using low level boot driver calls. It can still fail but at least has a fairly low probability of damaging the filesystem further. I suppose Linux could maybe dump to the swap partition or something.
Re:Good idea (Score:4, Insightful)
As AmiMoJo also noted, when you have a kernel panic all bets are off regarding which parts of the kernel are OK. If the behaviour of the disk driver or filesystem have been affected, it could damage your filesystem to try to write a kernel dump into a normal disk partition. It might work but it does seem a good idea to be properly paranoid. I didn't know that Windows uses a special reserved area of the boot drive - that does make sense as a solution!
There have been various systems for crash dumping under Linux, though. I think the de-facto solution (the one that was accepted by the kernel devs) ended up being kdump, which is based on kexec (kexec is "boot directly to a new kernel from an old kernel, without a reboot"). This allows full crash dumps with (hopefully) decent safety, so it is possible to do this if configured.
In kdump, you have a "spare" kernel loaded in some reserved memory and waiting to execute. When the primary kernel panics it will (if possible) begin executing the dump kernel, which is (hopefully) able to reinitialise the hardware and filesystem drivers, then write out the rest of memory to disk. I'm not sure how protected kdump's kernel is from whatever trashed the "main" kernel but there are things that would help - for instance, if they map its memory read only (or even keep it unmapped) so that somebody's buffer overflow can't just scribble on it during the crash.
Obviously, having a full kernel available to do the crashdump makes it easier to do other clever tricks, in principle - such as writing the dump out to a server on the network. That's not new, in that there used to be a kernel patch allowing a panicked kernel directly to write out a dump to network, it just seems easier to do it the kdump way, with a whole fresh kernel. Having a fully-working kernel, rather than one which is trying to restrict its behaviour, means you can rely on more kernel services - and probably just write your dumper code as a userspace program! Having just installed system-config-kdump on Fedora 20, I see that there's an option to dump to NFS, or to an SSH-able server - the latter would never be sanely doable from within the kernel but pretty easy from userspace.
Various distros do support kdump. I think it's often not enabled by default and does require a (comparatively small) amount of reserved RAM. So that's some motivation for basic QR code tracebacks. I suppose another reason is if they expect they can mostly decipher what happened from a traceback, without the dump being necessary - plus, with a bug report you can easily C&P a traceback.
This discussion has just inspired me to install the tools, so maybe I'll find out what it's like...