Re: [PATCH] signalfd: retrieve multiple signals with one read() call

[Davide Libenzi <davidel@xmailserver.org>]

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.


> 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.


- Davide