Refactor postmaster child process launching

Introduce new postmaster_child_launch() function that deals with the
differences in EXEC_BACKEND mode.

Refactor the mechanism of passing information from the parent to child
process. Instead of using different command-line arguments when
launching the child process in EXEC_BACKEND mode, pass a
variable-length blob of startup data along with all the global
variables. The contents of that blob depend on the kind of child
process being launched. In !EXEC_BACKEND mode, we use the same blob,
but it's simply inherited from the parent to child process.

Reviewed-by: Tristan Partin, Andres Freund
Discussion: https://www.postgresql.org/message-id/7a59b073-5b5b-151e-7ed3-8b01ff7ce9ef@iki.fi

10 files changed, 26 insertions, 24 deletions

diff --git a/src/include/postmaster/autovacuum.h b/src/include/postmaster/autovacuum.h
index 80cf4cdd969..cae1e8b3294 100644
--- a/src/include/postmaster/autovacuum.h
+++ b/src/include/postmaster/autovacuum.h
@@ -50,18 +50,14 @@ extern PGDLLIMPORT int Log_autovacuum_min_duration;
 /* Status inquiry functions */
 extern bool AutoVacuumingActive(void);
 
-/* Functions to start autovacuum process, called from postmaster */
+/* called from postmaster at server startup */
 extern void autovac_init(void);
-extern int	StartAutoVacLauncher(void);
-extern int	StartAutoVacWorker(void);
 
 /* called from postmaster when a worker could not be forked */
 extern void AutoVacWorkerFailed(void);
 
-#ifdef EXEC_BACKEND
-extern void AutoVacLauncherMain(int argc, char *argv[]) pg_attribute_noreturn();
-extern void AutoVacWorkerMain(int argc, char *argv[]) pg_attribute_noreturn();
-#endif
+extern void AutoVacLauncherMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
+extern void AutoVacWorkerMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 
 extern bool AutoVacuumRequestWork(AutoVacuumWorkItemType type,
 								  Oid relationId, BlockNumber blkno);
diff --git a/src/include/postmaster/auxprocess.h b/src/include/postmaster/auxprocess.h
index 3e443edde70..4e80b1cfec7 100644
--- a/src/include/postmaster/auxprocess.h
+++ b/src/include/postmaster/auxprocess.h
@@ -13,8 +13,6 @@
 #ifndef AUXPROCESS_H
 #define AUXPROCESS_H
 
-#include "miscadmin.h"
-
-extern void AuxiliaryProcessMain(BackendType auxtype) pg_attribute_noreturn();
+extern void AuxiliaryProcessMainCommon(void);
 
 #endif							/* AUXPROCESS_H */
diff --git a/src/include/postmaster/bgworker_internals.h b/src/include/postmaster/bgworker_internals.h
index 5e30525364b..9106a0ef3f0 100644
--- a/src/include/postmaster/bgworker_internals.h
+++ b/src/include/postmaster/bgworker_internals.h
@@ -55,6 +55,6 @@ extern void ForgetUnstartedBackgroundWorkers(void);
 extern void ResetBackgroundWorkerCrashTimes(void);
 
 /* Entry point for background worker processes */
-extern void BackgroundWorkerMain(void) pg_attribute_noreturn();
+extern void BackgroundWorkerMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 
 #endif							/* BGWORKER_INTERNALS_H */
diff --git a/src/include/postmaster/bgwriter.h b/src/include/postmaster/bgwriter.h
index b52dc19ef0b..407f26e5302 100644
--- a/src/include/postmaster/bgwriter.h
+++ b/src/include/postmaster/bgwriter.h
@@ -27,8 +27,8 @@ extern PGDLLIMPORT int CheckPointTimeout;
 extern PGDLLIMPORT int CheckPointWarning;
 extern PGDLLIMPORT double CheckPointCompletionTarget;
 
-extern void BackgroundWriterMain(void) pg_attribute_noreturn();
-extern void CheckpointerMain(void) pg_attribute_noreturn();
+extern void BackgroundWriterMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
+extern void CheckpointerMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 
 extern void RequestCheckpoint(int flags);
 extern void CheckpointWriteDelay(int flags, double progress);
diff --git a/src/include/postmaster/pgarch.h b/src/include/postmaster/pgarch.h
index 6135a9718d6..a7a417226b0 100644
--- a/src/include/postmaster/pgarch.h
+++ b/src/include/postmaster/pgarch.h
@@ -29,7 +29,7 @@
 extern Size PgArchShmemSize(void);
 extern void PgArchShmemInit(void);
 extern bool PgArchCanRestart(void);
-extern void PgArchiverMain(void) pg_attribute_noreturn();
+extern void PgArchiverMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 extern void PgArchWakeup(void);
 extern void PgArchForceDirScan(void);
 
diff --git a/src/include/postmaster/postmaster.h b/src/include/postmaster/postmaster.h
index 53f82bb5d43..333f81c2c52 100644
--- a/src/include/postmaster/postmaster.h
+++ b/src/include/postmaster/postmaster.h
@@ -13,6 +13,8 @@
 #ifndef _POSTMASTER_H
 #define _POSTMASTER_H
 
+#include "miscadmin.h"
+
 /* GUC options */
 extern PGDLLIMPORT bool EnableSSL;
 extern PGDLLIMPORT int SuperuserReservedConnections;
@@ -58,11 +60,9 @@ extern int	MaxLivePostmasterChildren(void);
 
 extern bool PostmasterMarkPIDForWorkerNotify(int);
 
-#ifdef EXEC_BACKEND
-
-extern pid_t postmaster_forkexec(int argc, char *argv[]);
-extern void SubPostmasterMain(int argc, char *argv[]) pg_attribute_noreturn();
+extern void BackendMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 
+#ifdef EXEC_BACKEND
 extern Size ShmemBackendArraySize(void);
 extern void ShmemBackendArrayAllocation(void);
 
@@ -71,6 +71,16 @@ extern void pgwin32_register_deadchild_callback(HANDLE procHandle, DWORD procId)
 #endif
 #endif
 
+/* defined in globals.c */
+extern struct ClientSocket *MyClientSocket;
+
+/* prototypes for functions in launch_backend.c */
+extern pid_t postmaster_child_launch(BackendType child_type, char *startup_data, size_t startup_data_len, struct ClientSocket *sock);
+const char *PostmasterChildName(BackendType child_type);
+#ifdef EXEC_BACKEND
+extern void SubPostmasterMain(int argc, char *argv[]) pg_attribute_noreturn();
+#endif
+
 /*
  * Note: MAX_BACKENDS is limited to 2^18-1 because that's the width reserved
  * for buffer references in buf_internals.h.  This limitation could be lifted
diff --git a/src/include/postmaster/startup.h b/src/include/postmaster/startup.h
index cf7a43e38cc..dde7ebde881 100644
--- a/src/include/postmaster/startup.h
+++ b/src/include/postmaster/startup.h
@@ -26,7 +26,7 @@
 extern PGDLLIMPORT int log_startup_progress_interval;
 
 extern void HandleStartupProcInterrupts(void);
-extern void StartupProcessMain(void) pg_attribute_noreturn();
+extern void StartupProcessMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 extern void PreRestoreCommand(void);
 extern void PostRestoreCommand(void);
 extern bool IsPromoteSignaled(void);
diff --git a/src/include/postmaster/syslogger.h b/src/include/postmaster/syslogger.h
index b26a2f29473..0f28ebcba55 100644
--- a/src/include/postmaster/syslogger.h
+++ b/src/include/postmaster/syslogger.h
@@ -86,9 +86,7 @@ extern int	SysLogger_Start(void);
 
 extern void write_syslogger_file(const char *buffer, int count, int destination);
 
-#ifdef EXEC_BACKEND
-extern void SysLoggerMain(int argc, char *argv[]) pg_attribute_noreturn();
-#endif
+extern void SysLoggerMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 
 extern bool CheckLogrotateSignal(void);
 extern void RemoveLogrotateSignalFiles(void);
diff --git a/src/include/postmaster/walsummarizer.h b/src/include/postmaster/walsummarizer.h
index ecb4ea37fba..ad346d0c119 100644
--- a/src/include/postmaster/walsummarizer.h
+++ b/src/include/postmaster/walsummarizer.h
@@ -21,7 +21,7 @@ extern PGDLLIMPORT int wal_summary_keep_time;
 
 extern Size WalSummarizerShmemSize(void);
 extern void WalSummarizerShmemInit(void);
-extern void WalSummarizerMain(void) pg_attribute_noreturn();
+extern void WalSummarizerMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 
 extern void GetWalSummarizerState(TimeLineID *summarized_tli,
 								  XLogRecPtr *summarized_lsn,
diff --git a/src/include/postmaster/walwriter.h b/src/include/postmaster/walwriter.h
index 60f23618cbd..5884d69fed1 100644
--- a/src/include/postmaster/walwriter.h
+++ b/src/include/postmaster/walwriter.h
@@ -18,6 +18,6 @@
 extern PGDLLIMPORT int WalWriterDelay;
 extern PGDLLIMPORT int WalWriterFlushAfter;
 
-extern void WalWriterMain(void) pg_attribute_noreturn();
+extern void WalWriterMain(char *startup_data, size_t startup_data_len) pg_attribute_noreturn();
 
 #endif							/* _WALWRITER_H */