[PATCH 1/2] libc: fix setting return value and errno in fallocate()

[Bernhard Reutner-Fischer]

On September 17, 2015 6:07:38 PM GMT+02:00, Rich Felker <dalias at libc.org> wrote:
>On Thu, Sep 17, 2015 at 03:56:55PM +0000, Yuriy Kolerov wrote:
>> Hi Waldemar and Bernhard.
>> 
>> First of all sorry for the absent of the detailed explanation of my
>> fixes. I'm going to send a second version of patches after our
>> discussion.
>> 
>> The problem is that fallocate does not pass LTP (Linux Test Project)
>> which checks return code and errno after fallocate execution. Then
>> I've found that fallocate in uClibc does not set errno thus I've
>> decided to fix it according to Linux manpage. But thanks to Bernhard
>> I've also found that posix_fallocate has another behavior:
>> "posix_fallocate() returns zero on success, or an error number on
>> failure. Note that errno is not set." And posix_fallocate in uClibc
>> refers to fallocate (oops). So my first patch is invalid in this
>> place: it's also necessary to change posix_fallocate and
>> posix_fallocate64 to meet requirements of POSIX (make it don't touch
>> errno and just return error code).
>
>Not-touching-errno is not a POSIX requirement. This is just a case of
>an over-aggressive man page documenting glibc-specific behavior that
>is not standard and should not be relied upon by applications.

Right.

> You can
>see here that there is no such requirement (by default any function in
>the standard is allowed to modify errno unless it's specified not to):

Where's that written?

http://pubs.opengroup.org/onlinepubs/9699919799/functions/errno.html

posix_fallocate does not mention it so errno is unspecified after such a call, AFAICS.

Thanks,

>
>http://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_fallocate.html
>
>Rich