Re: [PATCH v3] xen/common: add keyhandler to show Xen command line

[dmukhin@ford.com]

Thanks for taking a look!

On Tue, Aug 11, 2026 at 10:05:17AM +0200, Roger Pau Monné wrote:
> On Mon, Aug 10, 2026 at 04:04:01PM -0700, dmukhin@ford.com wrote:
> > From: Denis Mukhin <dmukhin@ford.com> 
> > 
> > Currently there's no way to print Xen command line on the emergency
> > console for debugging purposes when 'xl' is not unavailable.
> > 
> > Add new keyhander 'X' to do command line printout.
> > 
> > Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> > ---
> > Changes since v2:
> > - account for CONFIG_CMDLINE_OVERRIDE case
> > - use IS_ENABLED()
> > 
> > v2: https://lore.kernel.org/xen-devel/20260803070047.3097846-3-dmukhin@ford.com/
> > CI: https://gitlab.com/xen-project/people/dmukhin/xen/-/pipelines/2748655201
> > ---
> >  xen/common/kernel.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> > 
> > diff --git a/xen/common/kernel.c b/xen/common/kernel.c
> > index d1bef9ac2b2b..54a7ee6f68e5 100644
> > --- a/xen/common/kernel.c
> > +++ b/xen/common/kernel.c
> > @@ -5,6 +5,7 @@
> >   */
> >  
> >  #include <xen/init.h>
> > +#include <xen/keyhandler.h>
> >  #include <xen/lib.h>
> >  #include <xen/errno.h>
> >  #include <xen/param.h>
> > @@ -505,6 +506,25 @@ static int __init cf_check param_init(void)
> >  __initcall(param_init);
> >  #endif
> >  
> > +static void cf_check show_hypervisor_info(unsigned char key)
> > +{
> > +    printk("'%c' pressed -> showing hypervisor information\n", key);
> > +
> > +    if ( IS_ENABLED(CONFIG_CMDLINE_OVERRIDE) )
> > +        printk("Bootloader command line ignored (CONFIG_CMDLINE_OVERRIDE=y)\n");
> 
> Since we are there already, why not print the builtin command line
> using CONFIG_CMDLINE?

Will update.

> 
> > +    else
> > +        printk("Command line: %s\n", saved_cmdline);
> > +}
> > +
> > +static int __init cf_check misc_init(void)
> > +{
> > +    register_keyhandler('X', show_hypervisor_info,
> > +                        "show hypervisor information", 0);
> 
> "show hypervisor information" seems too generic to me, almost all
> debug keys could be defined by this sentence TBH.  I think this needs
> to be more specific, but I'm not sure what's the plan regarding this
> key.  Is there an intention to print more stuff here, or just the
> command line?  Knowing the full set of information to be printed might
> help come up with a better name.

I will update to "show_cmdline" since I originally planed to expose Xen
command line only so it is possible to better debug a system when dom0
becomes almost unresponsive.

> 
> Thanks, Roger.
> 

--
Denis