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

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

  

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.

So you need to do:

  errno = 0
  new_size = strtoull(argv[2], &tmp, 10);
  if ((errno) || (*tmp != '\0')) {
    ...
  }