Remove configure probe for fdatasync.

fdatasync() is in SUSv2, and all targeted Unix systems have it.  We have
a replacement function for Windows.

We retain the probe for the function declaration, which allows us to
supply the mysteriously missing declaration for macOS, and also for
Windows.  No need to keep a HAVE_FDATASYNC macro around.

Also rename src/port/fdatasync.c to win32fdatasync.c since it's only for
Windows.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA+hUKGJ3LHeP9w5Fgzdr4G8AnEtJ=z=p6hGDEm4qYGEUX5B6fQ@mail.gmail.com
Discussion: https://postgr.es/m/CA%2BhUKGJZJVO%3DiX%2Beb-PXi2_XS9ZRqnn_4URh0NUQOwt6-_51xQ%40mail.gmail.com

configure

@@ -16039,7 +16039,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in backtrace_symbols copyfile fdatasync getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
+for ac_func in backtrace_symbols copyfile getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
@@ -16929,12 +16929,6 @@ fi
  ;;
 esac
 
-  case " $LIBOBJS " in
-  *" fdatasync.$ac_objext "* ) ;;
-  *) LIBOBJS="$LIBOBJS fdatasync.$ac_objext"
- ;;
-esac
-
   case " $LIBOBJS " in
   *" getrusage.$ac_objext "* ) ;;
   *) LIBOBJS="$LIBOBJS getrusage.$ac_objext"
@@ -16977,6 +16971,12 @@ esac
  ;;
 esac
 
+  case " $LIBOBJS " in
+  *" win32fdatasync.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS win32fdatasync.$ac_objext"
+ ;;
+esac
+
   case " $LIBOBJS " in
   *" win32link.$ac_objext "* ) ;;
   *) LIBOBJS="$LIBOBJS win32link.$ac_objext"

configure.ac

@@ -1792,7 +1792,6 @@ LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 AC_CHECK_FUNCS(m4_normalize([
 	backtrace_symbols
 	copyfile
-	fdatasync
 	getifaddrs
 	getpeerucred
 	inet_pton
@@ -1928,7 +1927,6 @@ if test "$PORTNAME" = "win32"; then
   AC_CHECK_FUNCS(_configthreadlocale)
   AC_REPLACE_FUNCS(gettimeofday)
   AC_LIBOBJ(dirmod)
-  AC_LIBOBJ(fdatasync)
   AC_LIBOBJ(getrusage)
   AC_LIBOBJ(kill)
   AC_LIBOBJ(open)
@@ -1936,6 +1934,7 @@ if test "$PORTNAME" = "win32"; then
   AC_LIBOBJ(win32dlopen)
   AC_LIBOBJ(win32env)
   AC_LIBOBJ(win32error)
+  AC_LIBOBJ(win32fdatasync)
   AC_LIBOBJ(win32link)
   AC_LIBOBJ(win32ntdll)
   AC_LIBOBJ(win32pread)

src/backend/access/transam/xlog.c

@@ -168,9 +168,7 @@ const struct config_enum_entry sync_method_options[] = {
 #ifdef HAVE_FSYNC_WRITETHROUGH
 	{"fsync_writethrough", SYNC_METHOD_FSYNC_WRITETHROUGH, false},
 #endif
-#ifdef HAVE_FDATASYNC
 	{"fdatasync", SYNC_METHOD_FDATASYNC, false},
-#endif
 #ifdef O_SYNC
 	{"open_sync", SYNC_METHOD_OPEN, false},
 #endif
@@ -8015,12 +8013,10 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 				msg = _("could not fsync write-through file \"%s\": %m");
 			break;
 #endif
-#ifdef HAVE_FDATASYNC
 		case SYNC_METHOD_FDATASYNC:
 			if (pg_fdatasync(fd) != 0)
 				msg = _("could not fdatasync file \"%s\": %m");
 			break;
-#endif
 		case SYNC_METHOD_OPEN:
 		case SYNC_METHOD_OPEN_DSYNC:
 			/* not reachable */

src/backend/storage/file/fd.c

@@ -442,20 +442,12 @@ pg_fsync_writethrough(int fd)
 
 /*
  * pg_fdatasync --- same as fdatasync except does nothing if enableFsync is off
- *
- * Not all platforms have fdatasync; treat as fsync if not available.
  */
 int
 pg_fdatasync(int fd)
 {
 	if (enableFsync)
-	{
-#ifdef HAVE_FDATASYNC
 		return fdatasync(fd);
-#else
-		return fsync(fd);
-#endif
-	}
 	else
 		return 0;
 }

src/bin/pg_test_fsync/pg_test_fsync.c

@@ -331,7 +331,6 @@ test_sync(int writes_per_op)
 	printf(LABEL_FORMAT, "fdatasync");
 	fflush(stdout);
 
-#ifdef HAVE_FDATASYNC
 	if ((tmpfile = open(filename, O_RDWR | PG_BINARY, 0)) == -1)
 		die("could not open output file");
 	START_TIMER;
@@ -347,9 +346,6 @@ test_sync(int writes_per_op)
 	}
 	STOP_TIMER;
 	close(tmpfile);
-#else
-	printf(NA_FORMAT, _("n/a"));
-#endif
 
 /*
  * Test fsync

src/include/access/xlogdefs.h

@@ -67,8 +67,7 @@ typedef uint16 RepOriginId;
 /*
  * This chunk of hackery attempts to determine which file sync methods
  * are available on the current platform, and to choose an appropriate
- * default method.  We assume that fsync() is always available, and that
+ * default method.
- * configure determined whether fdatasync() is.
  *
  * Note that we define our own O_DSYNC on Windows, but not O_SYNC.
  */
@@ -76,10 +75,8 @@ typedef uint16 RepOriginId;
 #define DEFAULT_SYNC_METHOD		PLATFORM_DEFAULT_SYNC_METHOD
 #elif defined(O_DSYNC) && (!defined(O_SYNC) || O_DSYNC != O_SYNC)
 #define DEFAULT_SYNC_METHOD		SYNC_METHOD_OPEN_DSYNC
-#elif defined(HAVE_FDATASYNC)
-#define DEFAULT_SYNC_METHOD		SYNC_METHOD_FDATASYNC
 #else
-#define DEFAULT_SYNC_METHOD		SYNC_METHOD_FSYNC
+#define DEFAULT_SYNC_METHOD		SYNC_METHOD_FDATASYNC
 #endif
 
 #endif							/* XLOG_DEFS_H */

src/include/pg_config.h.in

@@ -170,9 +170,6 @@
 /* Define to 1 if you have the `explicit_bzero' function. */
 #undef HAVE_EXPLICIT_BZERO
 
-/* Define to 1 if you have the `fdatasync' function. */
-#undef HAVE_FDATASYNC
-
 /* Define to 1 if fseeko (and presumably ftello) exists and is declared. */
 #undef HAVE_FSEEKO
 

src/include/port/freebsd.h

@@ -5,6 +5,4 @@
  * would prefer open_datasync on FreeBSD 13+, but that is not a good choice on
  * many systems.
  */
-#ifdef HAVE_FDATASYNC
 #define PLATFORM_DEFAULT_SYNC_METHOD	SYNC_METHOD_FDATASYNC
-#endif

src/include/port/win32_port.h

@@ -83,14 +83,6 @@
 #define HAVE_FSYNC_WRITETHROUGH
 #define FSYNC_WRITETHROUGH_IS_FSYNC
 
-/*
- * We have a replacement for fdatasync() in src/port/fdatasync.c, which is
- * unconditionally used by MSVC and Mingw builds.
- */
-#ifndef HAVE_FDATASYNC
-#define HAVE_FDATASYNC
-#endif
-
 #define USES_WINSOCK
 
 /*

src/port/win32fdatasync.c

@@ -1,12 +1,12 @@
 /*-------------------------------------------------------------------------
  *
- * fdatasync.c
+ * win32fdatasync.c
  *	   Win32 fdatasync() replacement
  *
  *
- * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
  *
- * src/port/fdatasync.c
+ * src/port/win32fdatasync.c
  *
  *-------------------------------------------------------------------------
  */

src/tools/msvc/Mkvcbuild.pm

@@ -99,7 +99,7 @@ sub mkvcbuild
 	$solution = CreateSolution($vsVersion, $config);
 
 	our @pgportfiles = qw(
-	  chklocale.c explicit_bzero.c fdatasync.c
+	  chklocale.c explicit_bzero.c
 	  getpeereid.c getrusage.c inet_aton.c
 	  getaddrinfo.c gettimeofday.c inet_net_ntop.c kill.c open.c
 	  snprintf.c strlcat.c strlcpy.c dirmod.c noblock.c path.c
@@ -110,6 +110,7 @@ sub mkvcbuild
 	  strerror.c tar.c
 	  win32dlopen.c
 	  win32env.c win32error.c
+	  win32fdatasync.c
 	  win32link.c
 	  win32pread.c
 	  win32pwrite.c

src/tools/msvc/Solution.pm

@@ -252,7 +252,6 @@ sub GenerateFiles
 		HAVE_EDITLINE_READLINE_H                    => undef,
 		HAVE_EXECINFO_H                             => undef,
 		HAVE_EXPLICIT_BZERO                         => undef,
-		HAVE_FDATASYNC                              => 1,
 		HAVE_FSEEKO                                 => 1,
 		HAVE_FUNCNAME__FUNC                         => undef,
 		HAVE_FUNCNAME__FUNCTION                     => 1,