Check for STATUS_DELETE_PENDING on Windows.

1.  Update our open() wrapper to check for NT's STATUS_DELETE_PENDING
and translate it to Unix-like errors.  This is done with
RtlGetLastNtStatus(), which is dynamically loaded from ntdll.  A new
file win32ntdll.c centralizes lookup of NT functions, in case we decide
to add more in the future.

2.  Remove non-working code that was trying to do something similar for
stat(), and just reuse the open() wrapper code.  As a side effect,
stat() also gains resilience against "sharing violation" errors.

3.  Since stat() is used very early in process startup, remove the
requirement that the Win32 signal event has been created before
pgwin32_open_handle() is reached.  Instead, teach pg_usleep() to fall
back to a non-interruptible sleep if reached before the signal event is
available.

This could be back-patched, but for now it's in master only.  The
problem has apparently been with us for a long time and generated only a
few complaints.  Proposed patches trigger it more often, which led to
this investigation and fix.

Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Alexander Lakhin <exclusion@gmail.com>
Reviewed-by: Juan José Santamaría Flecha <juanjo.santamaria@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGJz_pZTF9mckn6XgSv69%2BjGwdgLkxZ6b3NWGLBCVjqUZA%40mail.gmail.com

1 files changed, 56 insertions, 48 deletions

diff --git a/src/port/open.c b/src/port/open.c
index 14c6debba91..7b52bd83c28 100644
--- a/src/port/open.c
+++ b/src/port/open.c
@@ -13,17 +13,20 @@
 
 #ifdef WIN32
 
+#define UMDF_USING_NTSTATUS
+
 #ifndef FRONTEND
 #include "postgres.h"
 #else
 #include "postgres_fe.h"
 #endif
 
+#include "port/win32ntdll.h"
+
 #include <fcntl.h>
 #include <assert.h>
 #include <sys/stat.h>
 
-
 static int
 openFlagsToCreateFileFlags(int openFlags)
 {
@@ -56,38 +59,25 @@ openFlagsToCreateFileFlags(int openFlags)
 }
 
 /*
- *	 - file attribute setting, based on fileMode?
+ * Internal function used by pgwin32_open() and _pgstat64().  When
+ * backup_semantics is true, directories may be opened (for limited uses).  On
+ * failure, INVALID_HANDLE_VALUE is returned and errno is set.
  */
-int
-pgwin32_open(const char *fileName, int fileFlags,...)
+HANDLE
+pgwin32_open_handle(const char *fileName, int fileFlags, bool backup_semantics)
 {
-	int			fd;
-	HANDLE		h = INVALID_HANDLE_VALUE;
+	HANDLE		h;
 	SECURITY_ATTRIBUTES sa;
 	int			loops = 0;
 
+	if (initialize_ntdll() < 0)
+		return INVALID_HANDLE_VALUE;
+
 	/* Check that we can handle the request */
 	assert((fileFlags & ((O_RDONLY | O_WRONLY | O_RDWR) | O_APPEND |
 						 (O_RANDOM | O_SEQUENTIAL | O_TEMPORARY) |
 						 _O_SHORT_LIVED | O_DSYNC | O_DIRECT |
 						 (O_CREAT | O_TRUNC | O_EXCL) | (O_TEXT | O_BINARY))) == fileFlags);
-#ifndef FRONTEND
-	Assert(pgwin32_signal_event != NULL);	/* small chance of pg_usleep() */
-#endif
-
-#ifdef FRONTEND
-
-	/*
-	 * Since PostgreSQL 12, those concurrent-safe versions of open() and
-	 * fopen() can be used by frontends, having as side-effect to switch the
-	 * file-translation mode from O_TEXT to O_BINARY if none is specified.
-	 * Caller may want to enforce the binary or text mode, but if nothing is
-	 * defined make sure that the default mode maps with what versions older
-	 * than 12 have been doing.
-	 */
-	if ((fileFlags & O_BINARY) == 0)
-		fileFlags |= O_TEXT;
-#endif
 
 	sa.nLength = sizeof(sa);
 	sa.bInheritHandle = TRUE;
@@ -102,6 +92,7 @@ pgwin32_open(const char *fileName, int fileFlags,...)
 						   &sa,
 						   openFlagsToCreateFileFlags(fileFlags),
 						   FILE_ATTRIBUTE_NORMAL |
+						   (backup_semantics ? FILE_FLAG_BACKUP_SEMANTICS : 0) |
 						   ((fileFlags & O_RANDOM) ? FILE_FLAG_RANDOM_ACCESS : 0) |
 						   ((fileFlags & O_SEQUENTIAL) ? FILE_FLAG_SEQUENTIAL_SCAN : 0) |
 						   ((fileFlags & _O_SHORT_LIVED) ? FILE_ATTRIBUTE_TEMPORARY : 0) |
@@ -140,38 +131,55 @@ pgwin32_open(const char *fileName, int fileFlags,...)
 		/*
 		 * ERROR_ACCESS_DENIED is returned if the file is deleted but not yet
 		 * gone (Windows NT status code is STATUS_DELETE_PENDING).  In that
-		 * case we want to wait a bit and try again, giving up after 1 second
-		 * (since this condition should never persist very long).  However,
-		 * there are other commonly-hit cases that return ERROR_ACCESS_DENIED,
-		 * so care is needed.  In particular that happens if we try to open a
-		 * directory, or of course if there's an actual file-permissions
-		 * problem.  To distinguish these cases, try a stat().  In the
-		 * delete-pending case, it will either also get STATUS_DELETE_PENDING,
-		 * or it will see the file as gone and fail with ENOENT.  In other
-		 * cases it will usually succeed.  The only somewhat-likely case where
-		 * this coding will uselessly wait is if there's a permissions problem
-		 * with a containing directory, which we hope will never happen in any
-		 * performance-critical code paths.
+		 * case, we'd better ask for the NT status too so we can translate it
+		 * to a more Unix-like error.  We hope that nothing clobbers the NT
+		 * status in between the internal NtCreateFile() call and CreateFile()
+		 * returning.
+		 *
+		 * If there's no O_CREAT flag, then we'll pretend the file is
+		 * invisible.  With O_CREAT, we have no choice but to report that
+		 * there's a file in the way (which wouldn't happen on Unix).
 		 */
-		if (err == ERROR_ACCESS_DENIED)
+		if (err == ERROR_ACCESS_DENIED &&
+			pg_RtlGetLastNtStatus() == STATUS_DELETE_PENDING)
 		{
-			if (loops < 10)
-			{
-				struct stat st;
-
-				if (stat(fileName, &st) != 0)
-				{
-					pg_usleep(100000);
-					loops++;
-					continue;
-				}
-			}
+			if (fileFlags & O_CREAT)
+				err = ERROR_FILE_EXISTS;
+			else
+				err = ERROR_FILE_NOT_FOUND;
 		}
 
 		_dosmaperr(err);
-		return -1;
+		return INVALID_HANDLE_VALUE;
 	}
 
+	return h;
+}
+
+int
+pgwin32_open(const char *fileName, int fileFlags,...)
+{
+	HANDLE		h;
+	int			fd;
+
+	h = pgwin32_open_handle(fileName, fileFlags, false);
+	if (h == INVALID_HANDLE_VALUE)
+		return -1;
+
+#ifdef FRONTEND
+
+	/*
+	 * Since PostgreSQL 12, those concurrent-safe versions of open() and
+	 * fopen() can be used by frontends, having as side-effect to switch the
+	 * file-translation mode from O_TEXT to O_BINARY if none is specified.
+	 * Caller may want to enforce the binary or text mode, but if nothing is
+	 * defined make sure that the default mode maps with what versions older
+	 * than 12 have been doing.
+	 */
+	if ((fileFlags & O_BINARY) == 0)
+		fileFlags |= O_TEXT;
+#endif
+
 	/* _open_osfhandle will, on error, set errno accordingly */
 	if ((fd = _open_osfhandle((intptr_t) h, fileFlags & O_APPEND)) < 0)
 		CloseHandle(h);			/* will not affect errno */