Re: [PATCH v2 2/2] xen/common: add keyhandler to show Xen command line

[Roger Pau Monné <roger@xxxxxxxxxxxxxx>]

On Fri, Aug 07, 2026 at 07:38:28PM -0700, dmukhin@xxxxxxxx wrote:
> On Fri, Aug 07, 2026 at 05:44:41PM -0700, Stefano Stabellini wrote:
> > On Mon, 3 Aug 2026, dmukhin@xxxxxxxx wrote:
> > > From: Denis Mukhin <dmukhin@xxxxxxxx> 
> > > 
> > > Currently there's no way to print Xen command line on the emergency
> > > console for debugging purposes (e.g. 'xl' is not available in dom0).
> > > 
> > > Add new keyhander 'X' to do command line printout.
> > > 
> > > Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
> > > ---
> > > v1: 
> > > https://lore.kernel.org/xen-devel/20260730061459.2702672-2-dmukhin@xxxxxxxx/
> > > 
> > > Changes since v1:
> > > - moved implementation into kernel.c
> > > ---
> > >  xen/common/kernel.c | 16 ++++++++++++++++
> > >  1 file changed, 16 insertions(+)
> > > 
> > > diff --git a/xen/common/kernel.c b/xen/common/kernel.c
> > > index d1bef9ac2b2b..9f334c92e3ab 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 +506,21 @@ 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);
> > > +    printk("Command line: %s\n", saved_cmdline);
> > 
> > if CONFIG_CMDLINE_OVERRIDE is defined, saved_cmdline is empty. We could
> > at least do this:
> > 
> > #ifdef CONFIG_CMDLINE_OVERRIDE
> >     printk("Bootloader command line ignored (CONFIG_CMDLINE_OVERRIDE=y)\n");
> > #else
> >     printk("Command line: %s\n", saved_cmdline);
> > #endif
> 
> Actually, CONFIG_CMDLINE can set the built-in command line which can be
> non-empty.
> 
> Perhaps, something like this:
> 
>     printk("Command line (built-in): %s\n", opt_builtin_cmdline);
> #ifndef CONFIG_CMDLINE_OVERRIDE
>     printk("Command line: %s\n", saved_cmdline);
> #endif

Aside from the remark from Oleksii, can you use IS_ENABLED() here
instead of preprocessor conditionals?

Thanks, Roger.