Re: [PATCH] qemu-options: Deprecate -old-param command line option

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Jan 27, 2025 at 12:31:13PM +0000, Peter Maydell wrote:
> The '-old-param' command line option is specific to Arm targets; it
> is very briefly documented as "old param mode".  What this option
> actually does is change the behaviour when directly booting a guest
> kernel, so that command line arguments are passed to the kernel using
> the extremely old "param_struct" ABI, rather than the newer ATAGS or
> even newer DTB mechanisms.
> 
> This support was added back in 2007 to support an old vendor kernel
> on the akita/terrier board types:
>  https://mail.gnu.org/archive/html/qemu-devel/2007-07/msg00344.html
> Even then, it was an out-of-date mechanism from the kernel's
> point of view -- the kernel has had a comment since 2001 marking
> it as deprecated. As of mid-2024, the kernel only retained
> param_struct support for the RiscPC and Footbridge platforms:
>  https://lore.kernel.org/linux-arm-kernel/2831c5a6-cfbf-4fe0-b51c-0396e5b0aeb7@app.fastmail.com/
> 
> None of the board types QEMU supports need param_struct support;
> mark this option as deprecated.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  docs/about/deprecated.rst | 13 +++++++++++++
>  system/vl.c               |  1 +
>  2 files changed, 14 insertions(+)

I think it is reasonable to remove this extreme special case given
the history around it

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


> 
> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
> index 29de49351d1..a4c7d642236 100644
> --- a/docs/about/deprecated.rst
> +++ b/docs/about/deprecated.rst
> @@ -68,6 +68,19 @@ configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is
>  marked deprecated since 9.0, users have to ensure that all the topology members
>  described with -smp are supported by the target machine.
>  
> +``-old-param`` option for booting Arm kernels via param_struct (since 10.0)
> +'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
> +
> +The ``-old-param`` command line option is specific to Arm targets:
> +it is used when directly booting a guest kernel to pass it the
> +command line and other information via the old ``param_struct`` ABI,
> +rather than the newer ATAGS or DTB mechanisms. This option was only
> +ever needed to support ancient kernels on some old board types
> +like the ``akita`` or ``terrier``; it has been deprecated in the
> +kernel since 2001. None of the board types QEMU supports need
> +``param_struct`` support, so this option has been deprecated and will
> +be removed in a future QEMU version.
> +
>  User-mode emulator command line arguments
>  -----------------------------------------
>  
> diff --git a/system/vl.c b/system/vl.c
> index c5678267182..32ee1ce7041 100644
> --- a/system/vl.c
> +++ b/system/vl.c
> @@ -3438,6 +3438,7 @@ void qemu_init(int argc, char **argv)
>                  nb_prom_envs++;
>                  break;
>              case QEMU_OPTION_old_param:
> +                warn_report("-old-param is deprecated");
>                  old_param = 1;
>                  break;
>              case QEMU_OPTION_rtc:
> -- 
> 2.34.1
> 
> 

With regards,
Daniel
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