Re: [PATCH] src/ext4_resize.c: set errno to 0 before the strtoull call

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella:

>   
>
> On 18/01/2022 02:27, xuyang2018.jy--- via Libc-alpha wrote:
>> on 2022/1/18 11:56, Theodore Ts'o wrote:
>>> On Tue, Jan 18, 2022 at 02:43:26AM +0000, xuyang2018.jy@fujitsu.com wrote:
>>>>> You're right of course, but out of curiosity, which C library are you
>>>>> using?
>>>> I use glibc-2.34.
>>>
>>> Hmm, ok.  I'm using glibc 2.31, and in this particular program, errno
>>> shouldn't have been set by any prior system call.  I'm guessing maybe
>>> it was something in crt0 which ended up setting errno?
>> It maybe a glibc bug.
>> I cc glibc mailing list and see whether they have met this problem.
>> 
>> @Florian
>> 
>> Now, I use glibc-2.34 and run the following program[1] but the errno is 
>> not 0 in the beginning. So is this a known bug on glibc-2.34(Theodore 
>> doesn't meet this problem on glicb-2.31)?
>> 
>> [1]https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/src/ext4_resize.c
>
> The errno should be only set on a failure, no function shall set errno
> to 0 (it is a POSIX definition which glibc adheres).  The application
> need to explicitly set errno to 0 before the function call to check if 
> an error occurs.

While this is true, I think errno should still be 0 at the start of the
program.

Thanks,
Florian