Re: APIs in New POSIX Edition

[Yaakov Selkowitz <yselkowi@redhat.com>]

On Thu, 2021-04-08 at 13:49 +0200, Corinna Vinschen wrote:
> On Apr  8 06:38, Joel Sherrill wrote:
> > On Thu, Apr 8, 2021, 6:19 AM Corinna Vinschen <vinschen@redhat.com> wrote:
> > 
> > > On Apr  7 18:26, Joel Sherrill wrote:
> > > > Hi
> > > > 
> > > > https://www.opengroup.org/austin/docs/austin_1110.pdf includes a set of
> > > new
> > > > methods to be added to the POSIX standard. RTEMS has a potential GSoC
> > > > student interested in working down the list for RTEMS. Some of these
> > > > make
> > > > sense to be implemented in newlib. All will end up being prototyped in
> > > > newlib headers somewhere.
> > > > 
> > > > > From the document and the formatting is completely lost.
> > > > 
> > > >  The additional APIs proposed by participants in the Austin Group that
> > > The
> > > > Open Group has agreed to sponsor are as follows:
> > > 
> > > > getentropy()
> > > > memmem()
> > > > reallocarray()
> > > > strlcat()
> > > > strlcpy()
> > > > wcslcat()
> > > > wcslcpy()
> > > 
> > > Already in newlib.
> > > 
> > > > ppoll()
> > > 
> > > Already defined in Cygwin.  We don't have a generic poll.h header in
> > > newlib.
> > > 
> > > > dladdr()
> > > 
> > > Already defined in Cygwin.  We don't have a generic dlfcn.h header in
> > > newlib.  It's questionable if this really belongs in newlib.
> > > 
> > > > getlocalename_l()
> > > > posix_getdents()
> > > > sig2str()
> > > > str2sig()
> > > 
> > > No worries as soon as the API is stable.
> > > 
> > > > pthread_cond_clockwait()
> > > > pthread_mutex_clocklock()
> > > > pthread_rwlock_clockrdlock()
> > > > pthread_rwlock_clockwrlock()
> > > > qsort_r()
> > > > sem_clockwait()
> > > 
> > > No worries, these APIs won't change compared to their already
> > > existing implementations in GLibc.
> > > 
> > 
> > Great.
> > 
> > What feature guard should these be behind? Will it change for the ones
> > already in place?
> 
> There will be a matching POSIX.1-2021 or so, given by date/month,
> with guards along the lines of _POSIX_C_SOURCE >= 202107L.

We have to wait and see what value glibc ends up using here:

https://sourceware.org/git/?p=glibc.git;a=blob;f=include/features.h;hb=HEAD

> APIS we already have should keep their current guard or'ed with
> the above _POSIX_C_SOURCE test.

_POSIX_C_SOURCE is only externally facing, function guards will use
(__POSIX_VISIBLE >= YYYYMM).

> APIs we already have but have no guard should get _DEFAULT_SOURCE
> or'ed with the above _POSIX_C_SOURCE test.

Let's consider each such case separately.

> There are also APIs which already exist per an older POSIX version,
> but which are not guarded.  I. e., the sem_xxx functions manipulating
> POSIX semaphores.  Those don't need aguard, because they have been
> introduced in conjunction with their own header, i. e., semaphore.h.
> 
> In these cases, the already existing ones still don't need a guard,
> just APIs added to the header will get the new _POSIX_C_SOURCE test.

__POSIX_VISIBLE, but yes.


-- 
Yaakov Selkowitz
Senior Software Engineer - Platform Enablement
Red Hat, Inc.