Re: strange dmesg output - RESOLVED

[Maxim Wexler-2]

Ok, this is too weird. While mucking around in the kernel I noticed
that the scroll back buffer wasn't set. So I configured it and gave it
128 bytes to play with. Sez I, well at least I'll be able to scroll
back to the start of all that verbiage. That's the only change I've
made since turning USB_STORAGE debugging off.

After a reboot, dmesg behaved and gives me a complete rundown on
startup all the way back to the prompt!

So, since in the digital world, things don't "just happen", can
someone enlighten me, or anyone else who's interested, in the
connection between the scrollback buffer and usb-storage, if any?

mw

[Alan McKinnon-2]

On Tuesday 27 October 2009 03:38:53 Maxim Wexler wrote:
> Ok, this is too weird. While mucking around in the kernel I noticed
> that the scroll back buffer wasn't set. So I configured it and gave it
> 128 bytes to play with.

It's 128 kilo bytes just btw :-)

> Sez I, well at least I'll be able to scroll
> back to the start of all that verbiage. That's the only change I've
> made since turning USB_STORAGE debugging off.
>
> After a reboot, dmesg behaved and gives me a complete rundown on
> startup all the way back to the prompt!
>
> So, since in the digital world, things don't "just happen", can
> someone enlighten me, or anyone else who's interested, in the
> connection between the scrollback buffer and usb-storage, if any?

There isn't a connection. Why do you think there is one?

You enabled scrollback so now the console has retained enough of the kernel
console output that you can scroll back to the beginning without using all
128K.



Symbol: VGACON_SOFT_SCROLLBACK_SIZE [=256]
Prompt: Scrollback Buffer Size (in KB)
  Defined at drivers/video/console/Kconfig:37
  Depends on: HAS_IOMEM && VT && VGACON_SOFT_SCROLLBACK

Symbol: VGACON_SOFT_SCROLLBACK [=y]
Prompt: Enable Scrollback Buffer in System RAM
  Defined at drivers/video/console/Kconfig:22
  Depends on: HAS_IOMEM && VT && VGA_CONSOLE

Symbol: USB_STORAGE [=m]
Prompt: USB Mass Storage support
  Defined at drivers/usb/storage/Kconfig:9
  Depends on: USB_SUPPORT && USB && SCSI

Symbol: USB_STORAGE_DEBUG [=n]
Prompt: USB Mass Storage verbose debug
  Defined at drivers/usb/storage/Kconfig:27
  Depends on: USB_SUPPORT && USB_STORAGE

Symbol: USB_SUPPORT [=y]
Prompt: USB support
  Defined at drivers/usb/Kconfig:5
  Depends on: HAS_IOMEM


--
alan dot mckinnon at gmail dot com

[Maxim Wexler-2]

>> So, since in the digital world, things don't "just happen", can
>> someone enlighten me, or anyone else who's interested, in the
>> connection between the scrollback buffer and usb-storage, if any?
>
>
> There isn't a connection. Why do you think there is one?

Because, before the scrollback buffer was configured,  when I ran
$dmesg|less the output, ie more that 2700 lines, that came up in the
console, all started with 'usb-storage'. After configuring the
scrollback buffer, there may have been a few usb-console lines but
certainly not 2700, and nothing else, one right after another.

I understand it makes no sense to say there is a connection but that
is what I saw.

It may have been intermittant. I notice with successive reboots of
2.6.30, /dev/sdb1,2, which contain /home and /var are sometimes not
found and not mounted; sometimes not found but mounted anyways;
sometimes found and mounted as per /etc/fstab. If it happens enough
times, I suppose a pattern will emerge but I haven't seen it yet.

mw

[Mick-10]

On Tuesday 27 October 2009 09:10:13 Alan McKinnon wrote:

> You enabled scrollback so now the console has retained enough of the kernel
> console output that you can scroll back to the beginning without using all
> 128K.
>
>
>
> Symbol: VGACON_SOFT_SCROLLBACK_SIZE [=256]
> Prompt: Scrollback Buffer Size (in KB)
>   Defined at drivers/video/console/Kconfig:37
>   Depends on: HAS_IOMEM && VT && VGACON_SOFT_SCROLLBACK
>
> Symbol: VGACON_SOFT_SCROLLBACK [=y]
> Prompt: Enable Scrollback Buffer in System RAM
>   Defined at drivers/video/console/Kconfig:22
>   Depends on: HAS_IOMEM && VT && VGA_CONSOLE

Not sure this is related with the OP's problem, I have noticed that on my
system I can scroll up in a console if it displays the output of a command,
e.g. ls, but I cannot scroll up on the boot messages.  Also, I cannot scroll
up on the log messages on VT12.  Is there something that I need to set up in
the kernel?  In the old days (perhaps different machine?) I used to be able to
scroll up in both.

$ cat /usr/src/linux/.config | grep SCROLLBACK
CONFIG_VGACON_SOFT_SCROLLBACK=y
CONFIG_VGACON_SOFT_SCROLLBACK_SIZE=128
--
Regards,
Mick

[Alan McKinnon-2]

On Wednesday 28 October 2009 03:50:56 Maxim Wexler wrote:

> >> So, since in the digital world, things don't "just happen", can
> >> someone enlighten me, or anyone else who's interested, in the
> >> connection between the scrollback buffer and usb-storage, if any?
> >
> > There isn't a connection. Why do you think there is one?
>
> Because, before the scrollback buffer was configured,  when I ran
> $dmesg|less the output, ie more that 2700 lines, that came up in the
> console, all started with 'usb-storage'. After configuring the
> scrollback buffer, there may have been a few usb-console lines but
> certainly not 2700, and nothing else, one right after another.
>
> I understand it makes no sense to say there is a connection but that
> is what I saw.
>
> It may have been intermittant. I notice with successive reboots of
> 2.6.30, /dev/sdb1,2, which contain /home and /var are sometimes not
> found and not mounted; sometimes not found but mounted anyways;
> sometimes found and mounted as per /etc/fstab. If it happens enough
> times, I suppose a pattern will emerge but I haven't seen it yet.

I think the presence or absence of your usb-storage debug output is related to
stuff being found or not found, and has nothing whatsoever to do with
scrollback.


--
alan dot mckinnon at gmail dot com

[Maxim Wexler-2]

>
> Not sure this is related with the OP's problem, I have noticed that on my
> system I can scroll up in a console if it displays the output of a command,
> e.g. ls, but I cannot scroll up on the boot messages.  Also, I cannot scroll
> up on the log messages on VT12.  Is there something that I need to set up in
> the kernel?  In the old days (perhaps different machine?) I used to be able
> to
> scroll up in both.

On my unit, /var/log/messages re-iterates F12. If I want to read  it I
use less, tail, grep in a terminal as root.

Also note, if you migrate away from the boot console and then come
back, it may not scrollback at all.  If I want to see what boot is
doing I scroll back immediately before running startx or moving to
another console.

HTH

[Mick-10]

On Wednesday 28 October 2009 20:10:52 Maxim Wexler wrote:
> > Not sure this is related with the OP's problem, I have noticed that on my
> > system I can scroll up in a console if it displays the output of a
> > command, e.g. ls, but I cannot scroll up on the boot messages.  Also, I
> > cannot scroll up on the log messages on VT12.  Is there something that I
> > need to set up in the kernel?  In the old days (perhaps different
> > machine?) I used to be able to
> > scroll up in both.

> Also note, if you migrate away from the boot console and then come
> back, it may not scrollback at all.  If I want to see what boot is
> doing I scroll back immediately before running startx or moving to
> another console.

I think that you may have put your finger on the problem here.  I used to run
startx from the console - now run xdm.  So it may have been that it worked
back then because I would scroll up before leaving the console.  However, I
seem to recall that it also worked with VT12.  May be I'm wrong, not sure.
--
Regards,
Mick

[Amit Dor-Shifer]

On Wednesday 28 October 2009 20:10:52 Maxim Wexler wrote:
 > > Not sure this is related with the OP's problem, I have noticed that
on my
 > > system I can scroll up in a console if it displays the output of a
 > > command, e.g. ls, but I cannot scroll up on the boot messages. Also, I
 > > cannot scroll up on the log messages on VT12. Is there something that I
 > > need to set up in the kernel? In the old days (perhaps different
 > > machine?) I used to be able to
 > > scroll up in both.

 > Also note, if you migrate away from the boot console and then come
 > back, it may not scrollback at all. If I want to see what boot is
 > doing I scroll back immediately before running startx or moving to
 > another console.

Maxim (or anyone else):
do you know what causes scrollback to be disabled once you move to a
different terminal?
Amit

[Alan McKinnon-2]

On Monday 09 November 2009 11:07:15 Amit Dor-Shifer wrote:

> On Wednesday 28 October 2009 20:10:52 Maxim Wexler wrote:
>  > > Not sure this is related with the OP's problem, I have noticed that
>
> on my
>
>  > > system I can scroll up in a console if it displays the output of a
>  > > command, e.g. ls, but I cannot scroll up on the boot messages. Also, I
>  > > cannot scroll up on the log messages on VT12. Is there something that
>  > > I need to set up in the kernel? In the old days (perhaps different
>  > > machine?) I used to be able to
>  > > scroll up in both.
>  >
>  > Also note, if you migrate away from the boot console and then come
>  > back, it may not scrollback at all. If I want to see what boot is
>  > doing I scroll back immediately before running startx or moving to
>  > another console.
>
> Maxim (or anyone else):
> do you know what causes scrollback to be disabled once you move to a
> different terminal?
> Amit
>

The scrollback buffer is global, not per-VT

So when you change VT, the buffer must go away other wise you have wrong text
on the wrong terminal.

--
alan dot mckinnon at gmail dot com