From ea61dab5b8be308bd82e56a5063f7acac70ad291 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.munro@gmail.com>
Date: Sun, 12 Dec 2021 14:13:35 +1300
Subject: [PATCH v2 1/2] Fix treatment of direct I/O in pg_test_fsync.

pg_test_fsync traditionally enabled O_DIRECT for the open_datasync and
open_sync tests.  In fact current releases of PostgreSQL only do that if
wal_level=minimal (less commonly used).  So, run the test both ways.

Discussion: https://postgr.es/m/CA%2BhUKGJZJVO%3DiX%2Beb-PXi2_XS9ZRqnn_4URh0NUQOwt6-_51xQ%40mail.gmail.com
---
 src/bin/pg_test_fsync/pg_test_fsync.c | 87 ++++++++++++++++++++++++---
 1 file changed, 79 insertions(+), 8 deletions(-)

diff --git a/src/bin/pg_test_fsync/pg_test_fsync.c b/src/bin/pg_test_fsync/pg_test_fsync.c
index ddabf64c58..1be017fcd5 100644
--- a/src/bin/pg_test_fsync/pg_test_fsync.c
+++ b/src/bin/pg_test_fsync/pg_test_fsync.c
@@ -303,12 +303,12 @@ test_sync(int writes_per_op)
 	printf(_("(in wal_sync_method preference order, except fdatasync is Linux's default)\n"));
 
 	/*
-	 * Test open_datasync if available
+	 * Test open_datasync direct if available
 	 */
-	printf(LABEL_FORMAT, "open_datasync");
+	printf(LABEL_FORMAT, "open_datasync (direct)");
 	fflush(stdout);
 
-#ifdef OPEN_DATASYNC_FLAG
+#if defined(OPEN_DATASYNC_FLAG) && (defined(O_DIRECT) || defined(F_NOCACHE))
 	if ((tmpfile = open_direct(filename, O_RDWR | O_DSYNC | PG_BINARY, 0)) == -1)
 	{
 		printf(NA_FORMAT, _("n/a*"));
@@ -333,6 +333,38 @@ test_sync(int writes_per_op)
 	printf(NA_FORMAT, _("n/a"));
 #endif
 
+	/*
+	 * Test open_datasync buffered if available
+	 */
+	printf(LABEL_FORMAT, "open_datasync (buffered)");
+	fflush(stdout);
+
+#ifdef OPEN_DATASYNC_FLAG
+	if ((tmpfile = open(filename, O_RDWR | O_DSYNC | PG_BINARY, 0)) == -1)
+	{
+		printf(NA_FORMAT, _("n/a*"));
+		fs_warning = true;
+	}
+	else
+	{
+		START_TIMER;
+		for (ops = 0; alarm_triggered == false; ops++)
+		{
+			for (writes = 0; writes < writes_per_op; writes++)
+				if (pg_pwrite(tmpfile,
+							  buf,
+							  XLOG_BLCKSZ,
+							  writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
+					die("write failed");
+		}
+		STOP_TIMER;
+		close(tmpfile);
+	}
+#else
+	printf(NA_FORMAT, _("n/a"));
+#endif
+
+
 /*
  * Test fdatasync if available
  */
@@ -409,13 +441,13 @@ test_sync(int writes_per_op)
 	printf(NA_FORMAT, _("n/a"));
 #endif
 
-/*
- * Test open_sync if available
- */
-	printf(LABEL_FORMAT, "open_sync");
+	/*
+	 * Test open_sync if available
+	 */
+	printf(LABEL_FORMAT, "open_sync (direct)");
 	fflush(stdout);
 
-#ifdef OPEN_SYNC_FLAG
+#if defined(OPEN_SYNC_FLAG) && (defined(O_DIRECT) || defined(F_NOCACHE))
 	if ((tmpfile = open_direct(filename, O_RDWR | OPEN_SYNC_FLAG | PG_BINARY, 0)) == -1)
 	{
 		printf(NA_FORMAT, _("n/a*"));
@@ -447,6 +479,45 @@ test_sync(int writes_per_op)
 	printf(NA_FORMAT, _("n/a"));
 #endif
 
+	/*
+	 * Test open_sync if available
+	 */
+	printf(LABEL_FORMAT, "open_sync (buffered)");
+	fflush(stdout);
+
+#ifdef OPEN_SYNC_FLAG
+	if ((tmpfile = open(filename, O_RDWR | OPEN_SYNC_FLAG | PG_BINARY, 0)) == -1)
+	{
+		printf(NA_FORMAT, _("n/a*"));
+		fs_warning = true;
+	}
+	else
+	{
+		START_TIMER;
+		for (ops = 0; alarm_triggered == false; ops++)
+		{
+			for (writes = 0; writes < writes_per_op; writes++)
+				if (pg_pwrite(tmpfile,
+							  buf,
+							  XLOG_BLCKSZ,
+							  writes * XLOG_BLCKSZ) != XLOG_BLCKSZ)
+
+					/*
+					 * This can generate write failures if the filesystem has
+					 * a large block size, e.g. 4k, and there is no support
+					 * for O_DIRECT writes smaller than the file system block
+					 * size, e.g. XFS.
+					 */
+					die("write failed");
+		}
+		STOP_TIMER;
+		close(tmpfile);
+	}
+#else
+	printf(NA_FORMAT, _("n/a"));
+#endif
+
+
 	if (fs_warning)
 	{
 		printf(_("* This file system and its mount options do not support direct\n"
-- 
2.30.2