Allow concurrent-safe open() and fopen() in frontend code for Windows

PostgreSQL uses a custom wrapper for open() and fopen() which is
concurrent-safe, allowing multiple processes to open and work on the
same file.  This has a couple of advantages:
- pg_test_fsync does not handle O_DSYNC correctly otherwise, leading to
false claims that disks are unsafe.
- TAP tests can run into race conditions when a postmaster and pg_ctl
open postmaster.pid, fixing some random failures in the buildfam.

pg_upgrade is one frontend tool using workarounds to bypass file locking
issues with the log files it generates, however the interactions with
pg_ctl are proving to be tedious to get rid of, so this is left for
later.

Author: Laurenz Albe
Reviewed-by: Michael Paquier, Kuntal Ghosh
Discussion: https://postgr.es/m/1527846213.2475.31.camel@cybertec.at
Discussion: https://postgr.es/m/16922.1520722108@sss.pgh.pa.us

src/bin/initdb/initdb.c

@@ -491,7 +491,15 @@ readfile(const char *path)
 	char	   *buffer;
 	int			c;
 
+#ifdef WIN32
+	/*
+	 * On Windows, we have to open the file in text mode so that carriage
+	 * returns are stripped.
+	 */
+	if ((infile = fopen(path, "rt")) == NULL)
+#else
 	if ((infile = fopen(path, "r")) == NULL)
+#endif
 	{
 		fprintf(stderr, _("%s: could not open file \"%s\" for reading: %s\n"),
 				progname, path, strerror(errno));

src/bin/pg_basebackup/pg_receivewal.c

@@ -288,7 +288,7 @@ FindStreamingStart(uint32 *tli)
 
 			snprintf(fullpath, sizeof(fullpath), "%s/%s", basedir, dirent->d_name);
 
-			fd = open(fullpath, O_RDONLY | PG_BINARY);
+			fd = open(fullpath, O_RDONLY | PG_BINARY, 0);
 			if (fd < 0)
 			{
 				fprintf(stderr, _("%s: could not open compressed file \"%s\": %s\n"),

src/bin/pg_verify_checksums/pg_verify_checksums.c

@@ -80,7 +80,7 @@ scan_file(const char *fn, BlockNumber segmentno)
 	int			f;
 	BlockNumber blockno;
 
-	f = open(fn, O_RDONLY | PG_BINARY);
+	f = open(fn, O_RDONLY | PG_BINARY, 0);
 	if (f < 0)
 	{
 		fprintf(stderr, _("%s: could not open file \"%s\": %s\n"),

src/common/file_utils.c

@@ -222,7 +222,7 @@ pre_sync_fname(const char *fname, bool isdir, const char *progname)
 {
 	int			fd;
 
-	fd = open(fname, O_RDONLY | PG_BINARY);
+	fd = open(fname, O_RDONLY | PG_BINARY, 0);
 
 	if (fd < 0)
 	{
@@ -283,7 +283,7 @@ fsync_fname(const char *fname, bool isdir, const char *progname)
 	 * unsupported operations, e.g. opening a directory under Windows), and
 	 * logging others.
 	 */
-	fd = open(fname, flags);
+	fd = open(fname, flags, 0);
 	if (fd < 0)
 	{
 		if (errno == EACCES || (isdir && errno == EISDIR))

src/include/port.h

@@ -249,11 +249,8 @@ extern bool rmtree(const char *path, bool rmtopdir);
 #define		O_DIRECT	0x80000000
 extern int	pgwin32_open(const char *, int,...);
 extern FILE *pgwin32_fopen(const char *, const char *);
-
-#ifndef FRONTEND
 #define		open(a,b,c) pgwin32_open(a,b,c)
 #define		fopen(a,b) pgwin32_fopen(a,b)
-#endif
 
 /*
  * Mingw-w64 headers #define popen and pclose to _popen and _pclose.  We want