Re: [Ksummit-discuss] [TECH TOPIC] printk redesign

[David Woodhouse <dwmw2@infradead.org>]

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On Mon, 2017-06-26 at 10:46 +0200, Jiri Kosina wrote:
> On Sat, 24 Jun 2017, Linus Torvalds wrote:
> 
> > 
> > > 
> > > It is how the embedded world operates, RS232, or now more often, RS232 
> > > with a built in USB-RS232 converter, so you use USB on the host.
> > I'm not saying that serial lines shouldn't be an option.
> > 
> > But for a *large* user base, they simply aren't.
> > 
> > On regular PC's, it's often not an option any more. Even in the data
> > center, it's often not an option any more.
> I don't really agree here. Yes, the mid-to-hig-end servers don't probably 
> contain the actual UART chip any more, but the vast majority of those have 
> somehting that's emulated in firmware, and actually do have a serial 
> console line connector (not the 9-pin one, but rather RJ-45 with either 
> Cisco or Yost pinout), which is then connected into serial-over-TCP 
> concentrator box, exposing the serial console over telnet (or some 
> proprietary client application). This is seen in DCs quite frequently.
> 
> Even machines that have very good IPMI support still ship with this.

Yeah, we definitely still have a "serial console" in the data centre,
even if it's not actually RS232 any more. Or indeed "serial".

You want to catch those failures where even kdump doesn't manage to
give you a viable report of the original crash? You'd better be
watching...

Even on regular PCs we have the USB debug ports which can serve the
same purpose.

But still, we're talking about printk being used for its original
$DEITY-intended purpose for debugging and diagnostic data. Not for the
random "hey, here's a channel I can abuse to send data up to userspace"
stuff. I heartily agree with Steven when he says that "printk is used
too freely".

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