Move walredo process code under pgxn in the main 'neon' repository.

- Refactor the way the WalProposerMain function is called when started
  with --sync-safekeepers. The postgres binary now explicitly loads
  the 'neon.so' library and calls the WalProposerMain in it. This is
  simpler than the global function callback "hook" we previously used.

- Move the WAL redo process code to a new library, neon_walredo.so,
  and use the same mechanism as for --sync-safekeepers to call the
  WalRedoMain function, when launched with --walredo argument.

- Also move the seccomp code to neon_walredo.so library. I kept the
  configure check in the postgres side for now, though.

Author: hlinnaka

src/backend/main/main.c

@@ -37,9 +37,9 @@
 
 #include "bootstrap/bootstrap.h"
 #include "common/username.h"
+#include "miscadmin.h"
 #include "port/atomics.h"
 #include "postmaster/postmaster.h"
-#include "replication/walpropshim.h"
 #include "storage/spin.h"
 #include "tcop/tcopprot.h"
 #include "utils/help_config.h"
@@ -56,6 +56,41 @@ static void init_locale(const char *categoryname, int category, const char *loca
 static void help(const char *progname);
 static void check_root(const char *progname);
 
+typedef int (*MainFunc) (int argc, char *argv[]);
+
+static int
+CallExtMain(char *library_name, char *main_func_name, int argc, char *argv[])
+{
+	MainFunc main_func;
+
+	/*
+	 * Perform just enough initialization that we can load external libraries
+	 */
+	InitStandaloneProcess(argv[0]);
+
+	SetProcessingMode(InitProcessing);
+
+	/*
+	 * Set default values for command-line options.
+	 */
+	InitializeGUCOptions();
+
+	/* Acquire configuration parameters */
+	if (!SelectConfigFiles(NULL, progname))
+		exit(1);
+
+	/*
+	 * Imitate we are early in bootstrap loading shared_preload_libraries;
+	 * neon extension sets PGC_POSTMASTER gucs requiring this.
+	 */
+	process_shared_preload_libraries_in_progress = true;
+
+	main_func = load_external_function(library_name, main_func_name, true, NULL);
+
+	process_shared_preload_libraries_in_progress = false;
+
+	return main_func(argc, argv);
+}
 
 /*
  * Any Postgres server process begins execution here.
@@ -200,11 +235,9 @@ main(int argc, char *argv[])
 		PostgresSingleUserMain(argc, argv,
 							   strdup(get_user_name_or_exit(progname)));
 	else if (argc > 1 && strcmp(argv[1], "--wal-redo") == 0)
-		WalRedoMain(argc, argv,
-					 NULL,		/* no dbname */
-					 strdup(get_user_name_or_exit(progname)));	/* does not return */
+		CallExtMain("neon_walredo", "WalRedoMain", argc, argv);
 	else if (argc > 1 && strcmp(argv[1], "--sync-safekeepers") == 0)
-		WalProposerSync(argc, argv);
+		CallExtMain("neon", "WalProposerSync", argc, argv);
 	else
 		PostmasterMain(argc, argv);
 	/* the functions above should not return */

src/backend/postmaster/Makefile

@@ -27,9 +27,4 @@ OBJS = \
 	syslogger.o \
 	walwriter.o
 
-ifeq ($(with_libseccomp),yes)
-OBJS += \
-	seccomp.o
-endif
-
 include $(top_srcdir)/src/backend/common.mk

src/backend/postmaster/bgworker.c

@@ -22,7 +22,6 @@
 #include "postmaster/postmaster.h"
 #include "replication/logicallauncher.h"
 #include "replication/logicalworker.h"
-#include "replication/walpropshim.h"
 #include "storage/dsm.h"
 #include "storage/ipc.h"
 #include "storage/latch.h"

src/backend/postmaster/postmaster.c

@@ -119,7 +119,6 @@
 #include "postmaster/syslogger.h"
 #include "replication/logicallauncher.h"
 #include "replication/walsender.h"
-#include "replication/walpropshim.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
 #include "storage/pg_shmem.h"

src/backend/postmaster/seccomp.c

@@ -22,8 +22,7 @@ OBJS = \
 	syncrep_gram.o \
 	walreceiver.o \
 	walreceiverfuncs.o \
-	walsender.o \
-	walpropcompat.o
+	walsender.o
 
 SUBDIRS = logical