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

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

On 11/1/2018 1:40 PM, Thomas Monjalon wrote:
> 01/11/2018 13:46, Ferruh Yigit:
>> 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.
> 
> OK
> 
> So I suggest only 2 minor changes:
> 	- strored -> stored
> 	- add a comment to explain that the error message from return value is enough

That is what I was trying to say in comment, we can't trust "ret" buffer but
need to use ret value which we can trust, I will re-visit the comment and fix typo

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