[LTP] [PATCH] timer_create01: accept kernel ENOTSUPP

[Thadeu Lima de Souza Cascardo]

On Wed, Oct 23, 2019 at 04:35:11PM +0200, Cyril Hrubis wrote:
> Hi!
> > > You are right. We want this to succeed with EOPNOTSUPP, as it's a valid error
> > > from kernel space.
> > 
> > Actually, man says that EOPNOTSUPP is only valid for socket operations.
> > So no, we should not go out of our way to explicitly check timer errors
> > against EOPNOTSUPP either. (It's also a waste of time because on Linux,
> > ENOTSUP == EOPNOTSUPP).
> 
> Beware that kernel defines ENOTSUP that is not equal to EOPNOTSUPP and
> in this case this value leaked to userspace leading to invalid userspace
> errno value.

That was ENOTSUPP (the internal kernel error, defined as 524). ENOTSUP, defined
as EOPNOTSUPP, is the userspace error I guess Martin is saying should not be
used either.

In that case, we need to fix the kernel to return EINVAL instead. Looking at
older changes here, I see commit 98d6f4dd84a134d942827584a3c5f67ffd8ec35f
("alarmtimer: return EINVAL instead of ENOTSUPP if rtcdev doesn't exist")
claiming exactly this. Though it was about clock_getres and clock_gettime,
quoting from that commit:

"
    Second, Posix and Linux man pages agree that clock_gettime and
    clock_getres should return EINVAL if clk_id argument is invalid.
    While the arugment that the clockid is valid, but just not supported
    on this hardware could be made, this is just a technicality that
    doesn't help userspace applicaitons, and only complicates error
    handling.
"

> 
> -- 
> Cyril Hrubis
> chrubis@suse.cz
> 
> -- 
> Mailing list info: https://lists.linux.it/listinfo/ltp