Re: [PATCH] libxl/x86: check return value of SHADOW_OP_SET_ALLOCATION domctl

[Jan Beulich <jbeulich@suse.com>]

On 02.07.2021 17:12, Jan Beulich wrote:
> On 02.07.2021 16:46, Anthony PERARD wrote:
>> On Fri, Jul 02, 2021 at 02:29:31PM +0200, Jan Beulich wrote:
>>> On 01.07.2021 11:36, Anthony PERARD wrote:
>>>> On Mon, Jun 28, 2021 at 01:47:03PM +0200, Jan Beulich wrote:
>>>>> --- a/tools/libs/light/libxl_x86.c
>>>>> +++ b/tools/libs/light/libxl_x86.c
>>>>> @@ -531,8 +531,18 @@ int libxl__arch_domain_create(libxl__gc
>>>>>      if (d_config->b_info.type != LIBXL_DOMAIN_TYPE_PV) {
>>>>>          unsigned long shadow = DIV_ROUNDUP(d_config->b_info.shadow_memkb,
>>>>>                                             1024);
>>>>> -        xc_shadow_control(ctx->xch, domid, XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION,
>>>>> -                          NULL, 0, &shadow, 0, NULL);
>>>>> +        int rc = xc_shadow_control(ctx->xch, domid,
>>>>
>>>> Could you use 'r' instead of 'rc' ? The later is reserved for libxl
>>>> error codes while the former is for system and libxc calls.
>>>
>>> Of course I can, but I did look at the rest of the function and
>>> found that it uses "ret" for the purpose of what you now say
>>> "rc" ought to be used for. Seeing "ret", I decided to avoid it
>>> (knowing you use different names for different kinds of return
>>> values). While I've switched to "r" for now, I'd be rather
>>> inclined to re-use "ret" instead. (Or actually, as per the
>>> remark further down, I can get away without any local variable
>>> then.)
>>
>> I know there's quite a few (many?) coding style issue in libxl. I'm
>> trying to prevent new issue without asking to fix the existing one.
>> The use of "ret" is an already existing issue, so I'm fine with it been
>> use in this patch for libxl error code in the function.
>>
>> BTW, you still need to store the return value of xc_shadow_control()
>> into a "r" variable before checking it for error.
> 
> Are you saying that
> 
>         if (xc_shadow_control(ctx->xch, domid,
>                               XEN_DOMCTL_SHADOW_OP_SET_ALLOCATION,
>                               NULL, 0, &shadow_mb, 0, NULL)) {
> 
> is not acceptable, style-wise?

Oh, there is indeed such a rule under "ERROR HANDLING". Which means ...

> If indeed you are, please disambiguate
> your statement above regarding the use of "ret": May I or may I not
> use it? IOW do I need to introduce "r", or can I get away with the
> existing local variables.

... I need this to be clarified.

Jan