Date: Sat, 10 Jan 2004 02:03:57 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Mark Linimon <linimon@lonesome.com> Cc: postmaster@netfang.net Subject: Re: Fwd: Re: ports/52016: New port: lang/harbour - AClipper-compatible compiler Message-ID: <20040110012527.S18300@gamplex.bde.org> In-Reply-To: <200401081510.39015.linimon@lonesome.com> References: <200401081510.39015.linimon@lonesome.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, 8 Jan 2004, Mark Linimon wrote:
> Hello. I'm a ports committer trying to help a submitter get a port ready
> for inclusion in the tree. This problem is clearly outside my league, so
> any suggestions on how I can help him would be appreciated.
> ---------- Forwarded Message ----------
>
> [mcl's cited compile error:]
>
> > ../../../../source/rtl/bsd/gcc/librtl.a(filesys.o): In function
> > `hb_fsCommit':
> > /usr/ports/lang/harbour/work/harbour/source/rtl/bsd/gcc/../../filesys.c:14
> >92: undefined reference to `fdatasync'
>
> [the submitter replied:]
>
> The hb_fsCommit function in filesys.c only attempts to use fdatasync if
> _POSIX_SYNCHRONIZED_IO is defined, so this error appears to be due to a bug
> in the POSIX library implementation in GCC on -current. The fdatasync
> function is a POSIX function that appears to me to be mandated to be
> present, even if unimplemented, if _POSIX_SYNCHRONIZED_IO is defined in
> unistd.h.
_POSIX_SYNCRONIZED_IO is defined as -1, which means that this optional
feature is not supported at all. From <sys/unistd.h>:
% /*
% * POSIX options and option groups we unconditionally do or don't
% * implement. Those options which are implemented (or not) entirely
% * in user mode are defined in <unistd.h>. Please keep this list in
% * alphabetical order.
% *
% * Anything which is defined as zero below **must** have an
% * implementation for the corresponding sysconf() which is able to
% * determine conclusively whether or not the feature is supported.
% * Anything which is defined as other than -1 below **must** have
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
% * complete headers, types, and function declarations as specified by
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
% * the POSIX standard; however, if the relevant sysconf() function
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
% * returns -1, the functions may be stubbed out.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
% */
I vaguely remember that fdatasync() is a subset of _POSIX_SYNCHRONIZED_IO.
fdatasync() is certainly not supported in FreeBSD, and the feature test
macro is correctly defined to indicate this.
The application's test of _POSIX_SYNCHRONIZED_IO is apparently broken.
It must do something like testing for (_POSIX_SYNCHRONIZED_IO + 0) !=
-1 at compile time (not just "#ifdef _POSIX_SYNCHRONIZED_IO"), and
according to the above, must also use sysconf() at runtime to see if
the feature actually works. I don't remember the latter requirement
in the standard, except in the following form:
- if a feature test macro has value 0, then the feature might not be
available and sysconf() must be used, as above.
- at least old standards seem to permit feature test macros to have no
value (they may be empty, or perhaps more bizarre). The "+ 0" in the
above is to handle this case, so that feature test with an empty value
work the same as ones with value 0.
- if a feature test macro has value > 0, then the feature is fully present
and need not be checked using sysconf().
POSIX feature tests macros are hard to use in their full generality (it
takes about a page of code per macro just to ifdef all the cases).
Practical applications would probably avoid most of these complications
by only supporting fully dynamic or fully static configuration. E.g.:
/* Fully static: */
/* Might "cache" the macro values in HAVE_FDATASYNC, etc. */
#if _POSIX_SYNCHRONIZED_IO + 0 > 0
fdatasync(fd);
#elif _POSIX_FSYNC + 0 > 0
fsync(fd);
#else
err(1, "system might not support fdatsync() or fsync()");
#endif
/* Fully dynamic: */
/* Might cache the sysconf() values in have_fdatasync, etc. */
if (sysconf(_SC_SYNCHRONIZED_IO) > 0)
fdatasync(fd);
else if (sysconf(_SC_FSYNC) > 0)
fdatasync(fd);
err(1, "system does not support fdatsync() or fsync()");
#endif
Bruce
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20040110012527.S18300>