kern/175674: sem_open() should use O_EXLOCK with open() instead of a separate flock() call

[Bruce Evans]

On Sun, 3 Feb 2013, Eitan Adler wrote:

> On 3 February 2013 16:00, Giorgos Keramidas <keramida at freebsd.org> wrote:
>> The following reply was made to PR kern/175674; it has been noted by GNATS.
>> > The best way to fix this is in kern_openat() in the kernel but this
>> > might cause compatibility issues.
>>
>>  Not sure if there would be serious compatibility problems if open() would
>>  automatically restart instead of returning EINTR.  It definitely seems a rather
>>  intrusive change though.
>
> I can not see major application breakage should open(3) be changed.
>
> That said,  I am confused by jilles' comment:
> http://pubs.opengroup.org/onlinepubs/000095399/functions/open.html
> open(3) is permitted to return EINTR.

Actually, open(3) is _required_ to return EINTR (if a signal occurs).

This hasn't changed since the old (2001) POSIX draft that I quoted in a
more detailed reply.  The wording is "shall fail...[with EINTR] if a
signal was caught during open()".  Only a perverse implementation of
weaselnix would justify not returning EINTR by not catching signals.

Bruce