DRM Kernel Log Renderer Proposed For Linux

[phoronix]

Phoronix: DRM Kernel Log Renderer Proposed For Linux

One of the long-standing proclaimed benefits of Direct Rendering Manager (DRM) graphics drivers for the Linux kernel was that it would be possible to have "Blue Screen of Death"-like error messages in cases of kernel issues. That feature is now closer to being realized while also advancing another goal of disabling VT support within the Linux kernel...

http://www.phoronix.com/vr.php?view=MTYyMzk

[xeekei]

I gather they're saying "no text during boot or shutdown/crash". What am I missing? Because that can't be what they're saying.

[Ericg]

I gather they're saying "no text during boot or shutdown/crash". What am I missing? Because that can't be what they're saying.

No, what they're saying is "If you disable VT's and do nothing else, you wont get debug info from Kernel Oops" (also some DE's apparently fail to load, who knew) because the VT subsystem registers a "console-driver" that can accept the crash output to display as text. If you're looking to replace or deprecate the VT subsystem then its important to have something else which handles all the important stuff the VT's did, this being one of those features. Enter drm-kernel-log, it registers a replacement console-driver so that you still get crash output from the kernel once a crash happens, even if the VT's are disabled.

[CTown]

So, the "Blue Screen Of Death" is considered a feature now? In that case, Linux should make its version purple. We don't want to copy "features" verbatim after all.

[Ericg]

So, the "Blue Screen Of Death" is considered a feature now? In that case, Linux should make its version purple. We don't want to copy "features" verbatim after all.

A longer and more detailed (or at least more text thats visible) crash output is a feature. Also, as I said above, its an issue of feature-parity.

[BSDude]

Why would you want the VT be disabled? As I understand disabling the VT subsystem will disable the ability to use TTY's? Correct me if I'm wrong!

[nanonyme]

Why would you want the VT be disabled? As I understand disabling the VT subsystem will disable the ability to use TTY's? Correct me if I'm wrong!

Yeah, I think you're right, mostly, and this led to my initial thought of protest. *However*, they seem not only to want to disable VT's but replace them, see "Combined with a proper user-space system-console". Technically it would be pretty interesting if VT-like functionality could be implemented completely in user-space using KMS. That way in-kernel functionality would simplify a lot and you might even get the accelerated non-graphical terminals back for free. (afaik currently VT's under KMS aren't properly accelerated which you typically don't notice if you use it for text only)

[doom_Oo7]

Why would you want the VT be disabled? As I understand disabling the VT subsystem will disable the ability to use TTY's? Correct me if I'm wrong!

Why would you want the VTs and TTYs enabled on :
- phones ?
- TV DivX / etc.. players ?
- Google glasses ?
- Steamboxes ?
- Car IVI systems ?
- Smart watch ?
- Any kind of hardware that doesn't have a keyboard and runs under Linux, i.e. certainly most of the linux ecosystem ?

[peppepz]

Why would you want the VT be disabled? As I understand disabling the VT subsystem will disable the ability to use TTY's? Correct me if I'm wrong!

I've heard that the VT code is somewhat limited, hard to maintain, doesn't support complex writing systems and doesn't fit very well with other modern kernel subsystems. However, from a user's point of view, VTs do work, they're easy to use, reliable, and they allow you to fix stuff without external help.

[robclark]

I've heard that the VT code is somewhat limited, hard to maintain, doesn't support complex writing systems and doesn't fit very well with other modern kernel subsystems. However, from a user's point of view, VTs do work, they're easy to use, reliable, and they allow you to fix stuff without external help.

VT switch is somewhat less reliable than people think if you have anything that uses graphics mode (since in that case VT switch becomes a cooperative thing between outgoing and incoming VT.. if the thing you are trying to switch away from is in a bad state (or in a breakpoint in gdb, etc).. well, opps, sorry, it won't work.