Hi Craig, On 03/24/2016 08:20 AM, Craig Howland wrote: > http://man7.org/linux/man-pages/man3/random.3.html contains an error with > respect to the feature test macro requirements. > > It says "_XOPEN_SOURCE >= 500 > || /* Glibc since 2.19: */ _DEFAULT_SOURCE > || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE" > > However, the POSIX-related requirement is not complete. According to POSIX, it > originated in issue 4 as an X/OPEN UNIX extension (see > http://pubs.opengroup.org/onlinepubs/9699919799/functions/random.html), and was > moved to BASE in issue 5. The GLIBC 2.12 on my RHEL6 system do seem to gate it > as POSIX says (see clips below), so it is only the man page in error. > > So the man page really should say "_XOPEN_SOURCE >= 500 > || _XOPEN_SOURCE_EXTENDED && _XOPEN_SOURCE > || /* Glibc since 2.19: */ _DEFAULT_SOURCE > || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE" > (I'm not totally certain of the right way for _XOPEN_SOURCE_EXTENDED to be used, > but you get the idea.) (Yes, what you show is technically accurate.) > Now perhaps this extra line was purposely left out based on a statement in > feature_test_macros(7) that says "since defining _XOPEN_SOURCE with a value of > 500 or more has the same effect as defining _XOPEN_SOURCE_EXTENDED, the latter > (obsolete) feature test macro is generally not described in the SYNOPSIS in man > pages." Yes. That is the reason. In the latest man-pages release (4.05), mention of _XOPEN_SOURCE_EXTENDED was removed from virtually every man page. > However, for this case it leaves out a user getting it with a version > older than 500. (The manual as-is is good for a new user, really, but it is not > good for a developer working on the proper gates in the code, or a user looking > at older code.) The problems here from my point of view are the following: * Maintaining the FTM information is an arduous task, especially when one tries to maintain historical information also (which I do try to do). * The FTM requirements shown in some man pages were growing very long. So long that they were an impediment to understanding in some cases. * _XOPEN_SOURCE_EXTENDED is indeed understood still by glibc. However, that FTM was last documented in a standard in 1995. For a long time now, no new code should have been trying to use it. * Re the last point: continuing to mention _XOPEN_SOURCE_EXTENDED in the man pages may actually mislead a few people into using that FTM! The above is why I removed mention of _XOPEN_SOURCE_EXTENDED from the man pages. It still seems like the right thing to do. If you have some strong couterarguments, I'd be interested to hear them. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
