[LTP] [PATCH v4 3/3] API: Remove TST_ERR usage from rtnetlink/netdevice

[Cyril Hrubis <chrubis@suse.cz>]

Hi!
> >>> The test author is guaranteed that the library will not set TST_ERR
> >>> except via the TEST macro and similar.
> >>
> >> Hi, who decided to guarantee this and where is the guarantee documented?
> 
> Guaranteeing that TST_RET and TST_ERR will not be modified makes sense
> for SAFE_SYSCALL()s because they will be used extensively throughout
> test code. But the case is not so clear for primarily setup()/cleanup()
> functions like the af_alg, rtnetlink and netdevice libraries. And note
> that the rtnetlink library allows you to check ACKs manually without
> calling the two functions which will modify TST_ERR.
> 
> So again, where is the extent of this guarantee documented? I haven't
> found any mention of it in the doc/ dir and Richie didn't add any docs
> changes in his patchset either. Documenting this is necessary for both
> test writers and library maintainers.

I guess that it should be added to
doc/library-api-writing-guidelines.txt but that is orthogonal to the
attempt to fix the the library code itself.

> >> Changing the return value to always return errno will be a major PITA
> >> because 95% of error handling happens after some safe_syscall() which
> >> clobbers errno by calling tst_brk() after failure. And if you only want
> >> to return error codes from rtnetlink ACK messages, then there's the
> >> problem what to return when a safe_syscall() fails during cleanup().
> > 
> > For the current code it would be as easy as:
> 
> That code will only result in RTNL_SEND_VALIDATE() always returning 0
> regardless of success or failure, except when tst_brk() terminates the
> whole program.

Ah right, we have to return non-zero if the tst_rtnl_send() or
tst_rtnl_rect() failed. I would be nice to propagete the errno properly,
which we do not do at the moment, but that looks like a lot of effort so
we may as well hardcode something non-zero there as well.

-- 
Cyril Hrubis
chrubis@suse.cz