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Check for fdatasync, and fall back to fsync if missing #55

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Check for fdatasync, and fall back to fsync if missing #55

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6 changes: 6 additions & 0 deletions config.h.in
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Original file line number Diff line number Diff line change
Expand Up @@ -240,6 +240,12 @@
/* Define if you have the flock function. */
#undef HAVE_FLOCK

/* Define if you have the fdatasync function. */
#undef HAVE_FDATASYNC

/* Define if the headers actually declare the fdatasync function. */
#undef HAVE_DECL_FDATASYNC

/* Define if you have the lockf function. */
#undef HAVE_LOCKF

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2 changes: 2 additions & 0 deletions configure.in
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Expand Up @@ -106,6 +106,8 @@ fi
AC_CHECK_FUNCS(getcwd gettimeofday mktime putenv strerror setenv unsetenv gethostname)
AC_CHECK_FUNCS(getopt_long)
AC_CHECK_FUNCS(mkstemp)
AC_CHECK_FUNCS(fdatasync)
AC_CHECK_DECLS(fdatasync)
AC_CHECK_FUNCS(flock lockf)
AC_CHECK_FUNCS(setlinebuf)
AC_CHECK_FUNCS(sigaction)
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8 changes: 8 additions & 0 deletions global.h
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Expand Up @@ -168,6 +168,14 @@
#endif

/* macros */
/* macOS has an fdatasync to link against, but doesn't declare or document it.
* Apple Clang suppresses the warning/error when calling it, which causes
* HAVE_FDATASYNC to be defined. But other compilers (including upstream Clang)
* don't. So we have to check both to see if we can safely use it. */
#if !defined(HAVE_FDATASYNC) || !HAVE_DECL_FDATASYNC
#define fdatasync(arg) fsync(arg)

@Rhys-T Rhys-T Jun 21, 2026 •
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Another option here, if you trust macOS's undocumented fdatasync function (which is what's currently being used if you build with Apple's tools), would be:

#if !HAVE_DECL_FDATASYNC
#if defined(__APPLE__) && defined(HAVE_FDATASYNC)
int fdatasync(int);
#else
#define fdatasync(arg) fsync(arg)
#endif
#endif

#endif

#ifndef HAVE_SETEUID
#define seteuid(arg) setresuid(-1,(arg),-1)
#endif
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