qemu-options: Deprecate -old-param command line option

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

Posted by Peter Maydell 2 months, 1 week ago

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Even then, it was an out-of-date mechanism from the kernel's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(+)

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

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

Posted by Daniel P. Berrangé 1 month, 4 weeks ago

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

Posted by Peter Maydell 1 month, 4 weeks ago

Ping for code review, please?

thanks
-- PMM

On Mon, 27 Jan 2025 at 12:31, Peter Maydell <peter.maydell@linaro.org> 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(+)
>
> 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:
> --