Re: [Xen-devel] [PATCH v2 48/52] xen: add hypercall for setting parameters at runtime

[Juergen Gross <jgross@xxxxxxxx>]

On 15/08/17 17:39, Jan Beulich wrote:
>>>> On 14.08.17 at 09:08, <jgross@xxxxxxxx> wrote:
>> --- a/xen/include/public/sysctl.h
>> +++ b/xen/include/public/sysctl.h
>> @@ -1096,6 +1096,23 @@ struct xen_sysctl_livepatch_op {
>>  typedef struct xen_sysctl_livepatch_op xen_sysctl_livepatch_op_t;
>>  DEFINE_XEN_GUEST_HANDLE(xen_sysctl_livepatch_op_t);
>>  
>> +/*
>> + * XEN_SYSCTL_set_parameter
>> + *
>> + * Change hypervisor parameters at runtime.
>> + * The input string is parsed similar to the boot parameters.
>> + */
>> +
>> +#define XEN_SET_PARAMETER_MAX_SIZE 1023
> 
> Does this really need to be in the public interface, i.e. isn't this limit
> an implementation detail?

Hmm, yes.

> 
>> +struct xen_sysctl_set_parameter {
>> +    XEN_GUEST_HANDLE_64(char) params;       /* IN: pointer to parameters. */
>> +    uint16_t size;                          /* IN: size of parameters. Max.
>> +                                               XEN_SET_PARAMETER_MAX_SIZE. 
>> */
> 
> You could even allow querying the size by passing in a null handle
> and returning the value in the size field.

Would this help in any way?

Maybe just returning E2BIG would be enough?

> 
>> +    uint16_t pad[3];                        /* IN: MUST be zero. */
> 
> But you don't check the field is zero afaics.

Right, I should do this.


Juergen

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