Re: [PATCH 1/8] rust: module_param: add StringParam type for C string parameters

[Petr Pavlu <petr.pavlu@suse.com>]

On 2/27/26 12:47 AM, Matthew Wood wrote:
> Introduce StringParam, a Copy wrapper around *const c_char that
> represents a string module parameter whose memory is managed by the
> kernel parameter subsystem.
> 
> StringParam provides:
>   - from_ptr(): construct from a raw C string pointer
>   - from_c_str(): construct from a static CStr (for compile-time
>     default values)
>   - null(): construct an unset/empty parameter
>   - as_cstr() / as_bytes(): safe accessors that return None when the
>     pointer is null
> 
> The type is marked Send + Sync because the underlying pointer is
> effectively 'static for the module's lifetime — the kernel guarantees
> the string memory remains valid while the module is loaded.

It is correct that module::args is currently valid for the module's
lifetime. However, I wonder if this is still needed and we're not
unnecessarily wasting memory. Since commit e180a6b7759a ("param: fix
charp parameters set via sysfs"), even charp parameters are kmalloc'ed,
unless they end up pointing into static_command_line when the specific
parameters are built into vmlinux and set during boot.

Similarly, if Rust modules eventually need to support parameters set via
sysfs, it will also be necessary to make copies.

-- 
Cheers,
Petr