Re: [dpdk-dev] [PATCH] eal: fix API to get error string

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 10/31/2018 6:43 PM, Thomas Monjalon wrote:
> 31/10/2018 19:26, Ferruh Yigit:
>> On 10/31/2018 6:26 PM, Ferruh Yigit wrote:
>>> On 10/31/2018 5:16 PM, Thomas Monjalon wrote:
>>>> 31/10/2018 18:19, Ferruh Yigit:
>>>>> rte_strerror uses strerror_r(), and strerror_r() has two version of it.
>>>>> - XSI-compliant version, (_POSIX_C_SOURCE >= 200112L) && !  _GNU_SOURCE
>>>>> - GNU-specific version
>>>>>
>>>>> Those two has different return types, so the exiting return type check
>>>>> is not correct for GNU-specific version.
>>>>>
>>>>> And this is causing failure in errno_autotest unit test.
>>>>>
>>>>> Adding different implementation for FreeBSD and Linux.
>>>>>
>>>>> Fixes: 016c32bd3e3d ("eal: cleanup strerror function")
>>>>> Cc: stable@dpdk.org
>>>>>
>>>>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
>>>>> ---
>>>>> --- a/lib/librte_eal/common/eal_common_errno.c
>>>>> +++ b/lib/librte_eal/common/eal_common_errno.c
>>>>>  		default:
>>>>> +#ifdef RTE_EXEC_ENV_BSDAPP
>>>>>  			if (strerror_r(errnum, ret, RETVAL_SZ) != 0)
>>>>>  				snprintf(ret, RETVAL_SZ, "Unknown error%s %d",
>>>>>  						sep, errnum);
>>>>> +#else
>>>>> +			/*
>>>>> +			 * _GNU_SOURCE version, error string is not always
>>>>> +			 * strored in "ret" buffer, need to use return value
>>>>> +			 */
>>>>> +			ret = strerror_r(errnum, ret, RETVAL_SZ);
>>>>> +#endif
>>>>
>>>> Why not use the return value in both cases?
>>>>
>>>> Why not writing an error message in Linux case?
>>>
>>> "man strerror_r" has more details, but briefly,
>>>
>>> The XSI-compliant strerror_r() function returns 0 on success. GNU one returns
>>> the pointer to string.
>>>
>>> The XSI-compliant can return an empty buffer, GNU one always return a string,
>>> either proper error string or "Unknown .." one.
> 
> You say "GNU one always return a string"
> The comment says:
> _GNU_SOURCE version, error string is not always strored in "ret" buffer

Yes, GNU one always return a char pointer to a string but that pointer may not
be in the "ret" buffer.

> 
> 
>> strerror_r() not portable. An alternative can be not using it at all...
> 
> It's fine to use it.
> 
>