On Sun, 20 May 2007 22:05:00 -0700 (PDT) Davide Libenzi <[email protected]> wrote:
> On Sun, 20 May 2007, Andrew Morton wrote:
>
> > > I think it fits the rule "buffer must be big enough for at least one sigingo".
> > > We use the special return 0; as indicator that the process we were
> > > monitoring signals, detached the sighand.
> > >
> >
> > hm. Kernel violates proper read() semantics in many places. Looks like we
> > just did it again.
>
> I think we can have the check that "if size == 0 return 0". The above
> cited return-0-on-detch would still apply for enough sized buffers. So:
>
> 1) size == 0, return 0 (POSIX wants this)
>
> 2) size < sizeof(signalfd_siginfo), return EINVAL
>
> 3) size >= sizeof(signalfd_siginfo) && DETACH, return 0
>
> The signalfd falls into what POSIX defined as "special file", and can
> return a lower-than-size result.
>
hm, well. I'd suggest that we do what makes most sense, rather than
warping things to try to obey the letter of posix.
>
> > Unless we just remove the __clear_user() altogether. Who said that "Unused
> > memebers should be zero"?
>
> Because it is a typically used value for still-unused/reserved members?
> Better than random values I think ;)
> Members validity is driven by si_code & SI_MASK anyway.
Sure. And it'd be a bit rude to return 128 from the read() but to only
have written to a few bytes of the user's memory.
otoh, only-writing-a-few-bytes will be usefully quicker than zapping the
whole 128b, particularly on small-cacheline CPUs.
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