No standardization on hostname max length

I was tracing a program in examples/ this evening and noticed that we have a myriad of different max hostname lengths ranging from 20 - 1024, and slight variations in handling gethostname():

https://gist.github.com/kmroz/6fb7699712d41abb4cd2ba9553163c82

I thought it might be a good idea to use, if available, what's in limits.h:HOST_NAME_MAX. Something like:

diff --git a/opal/include/opal_config_bottom.h b/opal/include/opal_config_bottom.hindex f906278..c2f1643 100644
--- a/opal/include/opal_config_bottom.h
+++ b/opal/include/opal_config_bottom.h
@@ -491,7 +491,14 @@ static inline uint16_t ntohs(uint16_t netvar) { return netvar; }      
#include <hostLib.h>

#ifndef MAXHOSTNAMELEN
-#define MAXHOSTNAMELEN 64
+/* From limits.h. Since we're using gethostname(), we add 1 to the max to allow
+ * for null termination.
+ */
+#ifdef HOST_NAME_MAX
+#define MAXHOSTNAMELEN HOST_NAME_MAX + 1
+#else
+#define MAXHOSTNAMELEN 64 + 1
+#endif
#endif
#endif

and sift through all callers of gethostname(). I have some concerns though:

1. I'm probably going to be stomping on components that may have an 'upstream' somewhere?
2. Non-POSIX systems might have some issue with this?

Perhaps this is barking up the wrong tree?

[rhc54]

we've been shamefully inconsistent on it - no harm in fixing it. any upstream conflicts are easily resolved