Re: [PATCH] libxc/PM: correct (not just) error handling in xc_get_cpufreq_para()

["Anthony PERARD" <anthony.perard@vates.tech>]

On Thu, Mar 27, 2025 at 02:32:04PM +0100, Jan Beulich wrote:
> HWP work made the cleanup of the "available governors" array
> conditional, neglecting the fact that the condition used may not be the

I don't know why the cleanup was made conditional, as long as the bounce
buffer is declared with DECLARE_NAMED_HYPERCALL_BOUNCE(),
xc_hypercall_bounce_post() can be called without issue (even if
..bounce_pre isn't used). Maybe it's all those "unlock_*" labels that is
misleading, a single "out" label which does the cleanup
unconditionally would be more than enough.

> condition that was used to allocate the buffer (as the structure field
> is updated upon getting back EAGAIN). Throughout the function, use the
> local variable being introduced to address that.
> 
> --- a/tools/libs/ctrl/xc_pm.c
> +++ b/tools/libs/ctrl/xc_pm.c
> @@ -212,31 +212,32 @@ int xc_get_cpufreq_para(xc_interface *xc
>      DECLARE_NAMED_HYPERCALL_BOUNCE(scaling_available_governors,
>  			 user_para->scaling_available_governors,
>  			 user_para->gov_num * CPUFREQ_NAME_LEN * sizeof(char), XC_HYPERCALL_BUFFER_BOUNCE_BOTH);
> -
> -    bool has_num = user_para->cpu_num &&
> -                     user_para->freq_num &&
> -                     user_para->gov_num;
> +    unsigned int in_gov_num = user_para->gov_num;
> +    bool has_num = user_para->cpu_num && user_para->freq_num;
>  
>      if ( has_num )

I think there's an issue here, this condition used to be true if
`gov_num` was not 0, even if `cpu_num` and `freq_num` was 0. That's not
the case anymore. Shouldn't `has_num` use also the value from
`gov_num`? Do we actually need `has_num`?

Thanks,

-- 

Anthony Perard | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech