Allow "in place" tablespaces.

Provide a developer-only GUC allow_in_place_tablespaces, disabled by
default.  When enabled, tablespaces can be created with an empty
LOCATION string, meaning that they should be created as a directory
directly beneath pg_tblspc.  This can be used for new testing scenarios,
in a follow-up patch.  Not intended for end-user usage, since it might
confuse backup tools that expect symlinks.

Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CA%2BhUKGKpRWQ9SxdxxDmTBCJoR0YnFpMBe7kyzY8SUQk%2BHeskxg%40mail.gmail.com

3 files changed, 46 insertions, 7 deletions

diff --git a/src/backend/commands/tablespace.c b/src/backend/commands/tablespace.c
index 3e154ec1056..7123b4069b4 100644
--- a/src/backend/commands/tablespace.c
+++ b/src/backend/commands/tablespace.c
@@ -87,6 +87,7 @@
 /* GUC variables */
 char	   *default_tablespace = NULL;
 char	   *temp_tablespaces = NULL;
+bool		allow_in_place_tablespaces = false;
 
 
 static void create_tablespace_directories(const char *location,
@@ -241,6 +242,7 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 	char	   *location;
 	Oid			ownerId;
 	Datum		newOptions;
+	bool		in_place;
 
 	/* Must be superuser */
 	if (!superuser())
@@ -266,12 +268,15 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 				(errcode(ERRCODE_INVALID_NAME),
 				 errmsg("tablespace location cannot contain single quotes")));
 
+	in_place = allow_in_place_tablespaces && strlen(location) == 0;
+
 	/*
 	 * Allowing relative paths seems risky
 	 *
-	 * this also helps us ensure that location is not empty or whitespace
+	 * This also helps us ensure that location is not empty or whitespace,
+	 * unless specifying a developer-only in-place tablespace.
 	 */
-	if (!is_absolute_path(location))
+	if (!in_place && !is_absolute_path(location))
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 				 errmsg("tablespace location must be an absolute path")));
@@ -590,16 +595,36 @@ create_tablespace_directories(const char *location, const Oid tablespaceoid)
 	char	   *linkloc;
 	char	   *location_with_version_dir;
 	struct stat st;
+	bool		in_place;
 
 	linkloc = psprintf("pg_tblspc/%u", tablespaceoid);
-	location_with_version_dir = psprintf("%s/%s", location,
+
+	/*
+	 * If we're asked to make an 'in place' tablespace, create the directory
+	 * directly where the symlink would normally go.  This is a developer-only
+	 * option for now, to facilitate regression testing.
+	 */
+	in_place = strlen(location) == 0;
+
+	if (in_place)
+	{
+		if (MakePGDirectory(linkloc) < 0 && errno != EEXIST)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not create directory \"%s\": %m",
+							linkloc)));
+	}
+
+	location_with_version_dir = psprintf("%s/%s", in_place ? linkloc : location,
 										 TABLESPACE_VERSION_DIRECTORY);
 
 	/*
 	 * Attempt to coerce target directory to safe permissions.  If this fails,
-	 * it doesn't exist or has the wrong owner.
+	 * it doesn't exist or has the wrong owner.  Not needed for in-place mode,
+	 * because in that case we created the directory with the desired
+	 * permissions.
 	 */
-	if (chmod(location, pg_dir_create_mode) != 0)
+	if (!in_place && chmod(location, pg_dir_create_mode) != 0)
 	{
 		if (errno == ENOENT)
 			ereport(ERROR,
@@ -648,13 +673,13 @@ create_tablespace_directories(const char *location, const Oid tablespaceoid)
 	/*
 	 * In recovery, remove old symlink, in case it points to the wrong place.
 	 */
-	if (InRecovery)
+	if (!in_place && InRecovery)
 		remove_tablespace_symlink(linkloc);
 
 	/*
 	 * Create the symlink under PGDATA
 	 */
-	if (symlink(location, linkloc) < 0)
+	if (!in_place && symlink(location, linkloc) < 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not create symbolic link \"%s\": %m",
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 85752817f83..effb9d03a03 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -46,6 +46,7 @@
 #include "catalog/storage.h"
 #include "commands/async.h"
 #include "commands/prepare.h"
+#include "commands/tablespace.h"
 #include "commands/trigger.h"
 #include "commands/user.h"
 #include "commands/vacuum.h"
@@ -1962,6 +1963,17 @@ static struct config_bool ConfigureNamesBool[] =
 	},
 
 	{
+		{"allow_in_place_tablespaces", PGC_SUSET, DEVELOPER_OPTIONS,
+			gettext_noop("Allows tablespaces directly inside pg_tblspc, for testing."),
+			NULL,
+			GUC_NOT_IN_SAMPLE
+		},
+		&allow_in_place_tablespaces,
+		false,
+		NULL, NULL, NULL
+	},
+
+	{
 		{"lo_compat_privileges", PGC_SUSET, COMPAT_OPTIONS_PREVIOUS,
 			gettext_noop("Enables backward compatibility mode for privilege checks on large objects."),
 			gettext_noop("Skips privilege checks when reading or modifying large objects, "
diff --git a/src/include/commands/tablespace.h b/src/include/commands/tablespace.h
index 97b0be35e52..323528ebb83 100644
--- a/src/include/commands/tablespace.h
+++ b/src/include/commands/tablespace.h
@@ -19,6 +19,8 @@
 #include "lib/stringinfo.h"
 #include "nodes/parsenodes.h"
 
+extern bool allow_in_place_tablespaces;
+
 /* XLOG stuff */
 #define XLOG_TBLSPC_CREATE		0x00
 #define XLOG_TBLSPC_DROP		0x10