Add pg_file_sync() to adminpack extension.

This function allows us to fsync the specified file or directory.
It's useful, for example, when we want to sync the file that
pg_file_write() writes out or that COPY TO exports the data into,
for durability.

Author: Fujii Masao
Reviewed-By: Julien Rouhaud, Arthur Zakirov, Michael Paquier, Atsushi Torikoshi
Discussion: https://www.postgresql.org/message-id/CAHGQGwGY8uzZ_k8dHRoW1zDcy1Z7=5GQ+So4ZkVy2u=nLsk=hA@mail.gmail.com

contrib/adminpack/Makefile

@@ -7,7 +7,8 @@ OBJS = \
 PG_CPPFLAGS = -I$(libpq_srcdir)
 
 EXTENSION = adminpack
-DATA = adminpack--1.0.sql adminpack--1.0--1.1.sql adminpack--1.1--2.0.sql
+DATA = adminpack--1.0.sql adminpack--1.0--1.1.sql adminpack--1.1--2.0.sql\
+	adminpack--2.0--2.1.sql
 PGFILEDESC = "adminpack - support functions for pgAdmin"
 
 REGRESS = adminpack

contrib/adminpack/adminpack--2.0--2.1.sql

@@ -0,0 +1,17 @@
+/* contrib/adminpack/adminpack--2.0--2.1.sql */
+
+-- complain if script is sourced in psql, rather than via ALTER EXTENSION
+\echo Use "ALTER EXTENSION adminpack UPDATE TO '2.1'" to load this file. \quit
+
+/* ***********************************************
+ * Administrative functions for PostgreSQL
+ * *********************************************** */
+
+/* generic file access functions */
+
+CREATE OR REPLACE FUNCTION pg_catalog.pg_file_sync(text)
+RETURNS void
+AS 'MODULE_PATHNAME', 'pg_file_sync'
+LANGUAGE C VOLATILE STRICT;
+
+REVOKE EXECUTE ON FUNCTION pg_catalog.pg_file_sync(text) FROM PUBLIC;

contrib/adminpack/adminpack.c

@@ -43,6 +43,7 @@ PG_MODULE_MAGIC;
 
 PG_FUNCTION_INFO_V1(pg_file_write);
 PG_FUNCTION_INFO_V1(pg_file_write_v1_1);
+PG_FUNCTION_INFO_V1(pg_file_sync);
 PG_FUNCTION_INFO_V1(pg_file_rename);
 PG_FUNCTION_INFO_V1(pg_file_rename_v1_1);
 PG_FUNCTION_INFO_V1(pg_file_unlink);
@@ -215,6 +216,30 @@ pg_file_write_internal(text *file, text *data, bool replace)
 	return (count);
 }
 
+/* ------------------------------------
+ * pg_file_sync
+ *
+ * We REVOKE EXECUTE on the function from PUBLIC.
+ * Users can then grant access to it based on their policies.
+ */
+Datum
+pg_file_sync(PG_FUNCTION_ARGS)
+{
+	char	   *filename;
+	struct stat	fst;
+
+	filename = convert_and_check_filename(PG_GETARG_TEXT_PP(0), false);
+
+	if (stat(filename, &fst) < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not stat file \"%s\": %m", filename)));
+
+	fsync_fname_ext(filename, S_ISDIR(fst.st_mode), false, ERROR);
+
+	PG_RETURN_VOID();
+}
+
 /* ------------------------------------
  * pg_file_rename - old version
  *

contrib/adminpack/adminpack.control

@@ -1,6 +1,6 @@
 # adminpack extension
 comment = 'administrative functions for PostgreSQL'
-default_version = '2.0'
+default_version = '2.1'
 module_pathname = '$libdir/adminpack'
 relocatable = false
 schema = pg_catalog

contrib/adminpack/expected/adminpack.out

@@ -56,6 +56,21 @@ RESET ROLE;
 REVOKE EXECUTE ON FUNCTION pg_file_write(text,text,bool) FROM regress_user1;
 REVOKE pg_read_all_settings FROM regress_user1;
 DROP ROLE regress_user1;
+-- sync
+SELECT pg_file_sync('test_file1'); -- sync file
+ pg_file_sync 
+--------------
+ 
+(1 row)
+
+SELECT pg_file_sync('pg_stat'); -- sync directory
+ pg_file_sync 
+--------------
+ 
+(1 row)
+
+SELECT pg_file_sync('test_file2'); -- not there
+ERROR:  could not stat file "test_file2": No such file or directory
 -- rename file
 SELECT pg_file_rename('test_file1', 'test_file2');
  pg_file_rename 
@@ -142,6 +157,8 @@ CREATE USER regress_user1;
 SET ROLE regress_user1;
 SELECT pg_file_write('test_file0', 'test0', false);
 ERROR:  permission denied for function pg_file_write
+SELECT pg_file_sync('test_file0');
+ERROR:  permission denied for function pg_file_sync
 SELECT pg_file_rename('test_file0', 'test_file0');
 ERROR:  permission denied for function pg_file_rename
 CONTEXT:  SQL function "pg_file_rename" statement 1

contrib/adminpack/sql/adminpack.sql

@@ -29,6 +29,11 @@ REVOKE EXECUTE ON FUNCTION pg_file_write(text,text,bool) FROM regress_user1;
 REVOKE pg_read_all_settings FROM regress_user1;
 DROP ROLE regress_user1;
 
+-- sync
+SELECT pg_file_sync('test_file1'); -- sync file
+SELECT pg_file_sync('pg_stat'); -- sync directory
+SELECT pg_file_sync('test_file2'); -- not there
+
 -- rename file
 SELECT pg_file_rename('test_file1', 'test_file2');
 SELECT pg_read_file('test_file1');  -- not there
@@ -58,6 +63,7 @@ CREATE USER regress_user1;
 SET ROLE regress_user1;
 
 SELECT pg_file_write('test_file0', 'test0', false);
+SELECT pg_file_sync('test_file0');
 SELECT pg_file_rename('test_file0', 'test_file0');
 SELECT pg_file_unlink('test_file0');
 SELECT pg_logdir_ls();

doc/src/sgml/adminpack.sgml

@@ -43,6 +43,13 @@
       Write, or append to, a text file
      </entry>
     </row>
+    <row>
+     <entry><function>pg_catalog.pg_file_sync(filename text)</function></entry>
+     <entry><type>void</type></entry>
+     <entry>
+      Flush a file or directory to disk
+     </entry>
+    </row>
     <row>
      <entry><function>pg_catalog.pg_file_rename(oldname text, newname text <optional>, archivename text</optional>)</function></entry>
      <entry><type>boolean</type></entry>
@@ -79,6 +86,18 @@
   Returns the number of bytes written.
  </para>
 
+ <indexterm>
+  <primary>pg_file_sync</primary>
+ </indexterm>
+ <para>
+  <function>pg_file_sync</function> fsyncs the specified file or directory
+  named by <parameter>filename</parameter>.  An error is thrown
+  on failure (e.g., the specified file is not present). Note that
+  <xref linkend="guc-data-sync-retry"/> has no effect on this function,
+  and therefore a PANIC-level error will not be raised even on failure to
+  flush database files.
+ </para>
+
  <indexterm>
   <primary>pg_file_rename</primary>
  </indexterm>

src/backend/storage/file/fd.c

@@ -319,7 +319,6 @@ static void pre_sync_fname(const char *fname, bool isdir, int elevel);
 static void datadir_fsync_fname(const char *fname, bool isdir, int elevel);
 static void unlink_if_exists_fname(const char *fname, bool isdir, int elevel);
 
-static int	fsync_fname_ext(const char *fname, bool isdir, bool ignore_perm, int elevel);
 static int	fsync_parent_path(const char *fname, int elevel);
 
 
@@ -3376,7 +3375,7 @@ unlink_if_exists_fname(const char *fname, bool isdir, int elevel)
  *
  * Returns 0 if the operation succeeded, -1 otherwise.
  */
-static int
+int
 fsync_fname_ext(const char *fname, bool isdir, bool ignore_perm, int elevel)
 {
 	int			fd;

src/include/storage/fd.h

@@ -145,6 +145,7 @@ extern int	pg_fsync_writethrough(int fd);
 extern int	pg_fdatasync(int fd);
 extern void pg_flush_data(int fd, off_t offset, off_t amount);
 extern void fsync_fname(const char *fname, bool isdir);
+extern int	fsync_fname_ext(const char *fname, bool isdir, bool ignore_perm, int elevel);
 extern int	durable_rename(const char *oldfile, const char *newfile, int loglevel);
 extern int	durable_unlink(const char *fname, int loglevel);
 extern int	durable_link_or_rename(const char *oldfile, const char *newfile, int loglevel);