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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

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

Other than that it is fine for me



> +}
> +
> +static int __init cf_check misc_init(void)
> +{
> +    register_keyhandler('X', show_hypervisor_info,
> +                        "show hypervisor information", 0);
> +
> +    return 0;
> +}
> +__initcall(misc_init);
> +
>  static long xenver_varbuf_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
>  {
>      struct xen_varbuf user_str;
> -- 
> 2.54.0
>