Xen devel - Jun 2010 - Can I use SGI''s kdb with a dom0 pv-ops kernel?

I asked this a few weeks ago but didn''t get a response, so at the risk
of
being a nag, I''ll abbreviate and restate.

I know there are other Xen specific debuggers, but I want to know if
there''s
any reason why SGI''s kdb, http://oss.sgi.com/projects/kdb, should not
be
included in a dom0 pv-ops kernel?

While the patches apply cleanly and build, the result is that one drops into
kdb on an oops the serial keyboard is non-functional.
Is this a problem inherent in including an incompatible debugger, or perhaps
just something wrong in a .config?

Does anyone else use this debugger for dom0 work ?

Thanks

-Bruce


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On Tue, Jun 29, 2010 at 03:05:42PM -0700, Bruce Edge
wrote:
> I asked this a few weeks ago but didn''t get a response, so at the
risk of
> being a nag, I''ll abbreviate and restate.
> 
> I know there are other Xen specific debuggers, but I want to know if
there''s
> any reason why SGI''s kdb, http://oss.sgi.com/projects/kdb, should
not be
> included in a dom0 pv-ops kernel?
Upstream is integrating one that I think is in 2.6.33
or 2.6.34. So when we rev up that we will get it for free.
> 
> While the patches apply cleanly and build, the result is that one drops
into
> kdb on an oops the serial keyboard is non-functional.
> Is this a problem inherent in including an incompatible debugger, or
perhaps
> just something wrong in a .config?
What is your serial setup? Are you using the serial console also for
Xen? Is the serial console that Dom0 sees usuable outside kdb? As in,
can you use a null modem connection and poke Dom0 via that?
> 
> Does anyone else use this debugger for dom0 work ?
I haven''t used it.

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On Wed, Jun 30, 2010 at 9:11 AM, Konrad Rzeszutek Wilk <
konrad.wilk@oracle.com> wrote:
> On Tue, Jun 29, 2010 at 03:05:42PM -0700, Bruce Edge wrote:
> > I asked this a few weeks ago but didn''t get a response, so at
the risk of
> > being a nag, I''ll abbreviate and restate.
> >
> > I know there are other Xen specific debuggers, but I want to know if
> there''s
> > any reason why SGI''s kdb, http://oss.sgi.com/projects/kdb,
should not be
> > included in a dom0 pv-ops kernel?
>
> Upstream is integrating one that I think is in 2.6.33
> or 2.6.34. So when we rev up that we will get it for free.
>
Which upstream source is doing this integration? I''m not seeing any
reference to it on

 http://kernelnewbies.org/Linux_2_6_33 or
http://kernelnewbies.org/Linux_2_6_34

> >
> > While the patches apply cleanly and build, the result is that one
drops
> into
> > kdb on an oops the serial keyboard is non-functional.
> > Is this a problem inherent in including an incompatible debugger, or
> perhaps
> > just something wrong in a .config?
>
> What is your serial setup?

Virtual direct connect via iLO.

> Are you using the serial console also for Xen?

Yes

> Is the serial console that Dom0 sees usuable outside kdb?

Yes

> As in, can you use a null modem connection and poke Dom0 via that?
>
Yep. The main connection to these boxes is the serial port. The kernel
cmdline has "console=hvc0,115200n8" so I get boot output on it,
I''m using
 "exec /sbin/getty -8 38400 hvc0" to get a login on the serial
console,
which works fine. The 3xCtrl-A also works.
It''s only KDB that doesn''t like it. It appears kdb can output
to the console
but cannot read from it.

These are the kdb patch files I used: (from http://oss.sgi.com/projects/kdb)

-r--r--r-- 1 bedge wlvusers 199234 2010-06-22 11:22
kdb-v4.4-2.6.32-common-3.bz2
-r--r--r-- 1 bedge wlvusers 136442 2010-06-22 11:22
kdb-v4.4-2.6.32-x86-3.bz2

.config changes:

CONFIG_KDB=y
CONFIG_KDB_MODULES=y
# CONFIG_KDB_OFF is not set
CONFIG_KDB_CONTINUE_CATASTROPHIC=2


> >
> > Does anyone else use this debugger for dom0 work ?
>
> I haven''t used it.
>
Thanks for the info Konrad.

-Bruce


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On Wed, Jun 30, 2010 at 09:44:46AM -0700, Bruce Edge
wrote:
> On Wed, Jun 30, 2010 at 9:11 AM, Konrad Rzeszutek Wilk <
> konrad.wilk@oracle.com> wrote:
> 
> > On Tue, Jun 29, 2010 at 03:05:42PM -0700, Bruce Edge wrote:
> > > I asked this a few weeks ago but didn''t get a response,
so at the risk of
> > > being a nag, I''ll abbreviate and restate.
> > >
> > > I know there are other Xen specific debuggers, but I want to know
if
> > there''s
> > > any reason why SGI''s kdb,
http://oss.sgi.com/projects/kdb, should not be
> > > included in a dom0 pv-ops kernel?
> >
> > Upstream is integrating one that I think is in 2.6.33
> > or 2.6.34. So when we rev up that we will get it for free.
> >
> 
> Which upstream source is doing this integration? I''m not seeing
any
> reference to it on
> 
>  http://kernelnewbies.org/Linux_2_6_33 or
> http://kernelnewbies.org/Linux_2_6_34
I am getting them confused. Here is what I see:

it dc7d552705215ac50a0617fcf51bb9c736255b8e
Author: Jason Wessel <jason.wessel@windriver.com>
Date:   Thu Apr 17 20:05:37 2008 +0200

    kgdb: core
    
    kgdb core code. Handles the protocol and the arch details.


which looks to be in kernel/kgdb.c. You need to have CONFIG_KGDB enabled
for it and some of the Linux command line paramters. That is not the SGI
one but the other one. Is the KGDB not working (or you just are more
comfortable with teh SGI one?)

> > As in, can you use a null modem connection and poke Dom0 via that?
> >
> 
> Yep. The main connection to these boxes is the serial port. The kernel
> cmdline has "console=hvc0,115200n8" so I get boot output on it,
I''m using
>  "exec /sbin/getty -8 38400 hvc0" to get a login on the serial
console,
> which works fine. The 3xCtrl-A also works.
I wonder if the problem you are hitting is that you are using the hvc0
driver. Not the real serial driver. Which means that the hvc0 driver
isn''t picking up any of your input b/c its workqueue has been
effectivly
terminated.

One way to go around this is to not use the serial console for Xen and
have the Dom0 use it exclusivly. Which means you would be doing
''console=ttyS0,38400''. At least that is the theory -  I am not
sure
if Xen will allow you to do that.

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>>> On 30.06.10 at 18:44, Bruce Edge <bruce.edge@gmail.com>
wrote:
>> Are you using the serial console also for Xen?
> 
> 
> Yes
That is your problem, I would assume, unless you taught kdb''s serial
driver to use the Xen specific replacement (i.e. not going directly to
the hardware serial port).

Jan 


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