Allow "in place" tablespaces.

This is a backpatch to branches 10-14 of the following commits:

7170f2159fb2 Allow "in place" tablespaces.
c6f2f01611d4 Fix pg_basebackup with in-place tablespaces.
f6f0db4d6240 Fix pg_tablespace_location() with in-place tablespaces
7a7cd84893e0 doc: Remove mention to in-place tablespaces for pg_tablespace_location()
5344723755bd Remove unnecessary Windows-specific basebackup code.

In-place tablespaces were introduced as a testing helper mechanism, but
they are going to be used for a bugfix in WAL replay to be backpatched
to all stable branches.

I (Álvaro) had to adjust some code to account for lack of
get_dirent_type() in branches prior to 14.

Author: Thomas Munro <thomas.munro@gmail.com>
Author: Michaël Paquier <michael@paquier.xyz>
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/20220722081858.omhn2in5zt3g4nek@alvherre.pgsql

1 files changed, 32 insertions, 7 deletions

diff --git a/src/backend/commands/tablespace.c b/src/backend/commands/tablespace.c
index f060c245995..5a60d8dd046 100644
--- a/src/backend/commands/tablespace.c
+++ b/src/backend/commands/tablespace.c
@@ -88,6 +88,7 @@
 /* GUC variables */
 char	   *default_tablespace = NULL;
 char	   *temp_tablespaces = NULL;
+bool		allow_in_place_tablespaces = false;
 
 
 static void create_tablespace_directories(const char *location,
@@ -242,6 +243,7 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 	char	   *location;
 	Oid			ownerId;
 	Datum		newOptions;
+	bool		in_place;
 
 	/* Must be super user */
 	if (!superuser())
@@ -267,12 +269,15 @@ 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")));
@@ -593,16 +598,36 @@ 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,
@@ -651,13 +676,13 @@ 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",