From 71d670eec45d0c7f9bfa6684e112b8bf5d6552fe Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryzbyj@telsasoft.com>
Date: Sat, 18 Dec 2021 22:51:01 -0600
Subject: [PATCH 3/4] errcontext if server fails to start due to library GUCs

---
 src/backend/utils/fmgr/dfmgr.c    | 21 ++++++++++++++++-----
 src/backend/utils/init/miscinit.c |  2 +-
 src/include/fmgr.h                |  1 +
 3 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index b03017f6275..fd8371cb582 100644
--- a/src/backend/utils/fmgr/dfmgr.c
+++ b/src/backend/utils/fmgr/dfmgr.c
@@ -76,7 +76,7 @@ static DynamicFileList *file_tail = NULL;
 
 char	   *Dynamic_library_path;
 
-static void *internal_load_library(const char *libname);
+static void *internal_load_library(const char *libname, const char *gucname);
 static void incompatible_module_error(const char *libname,
 									  const Pg_magic_struct *module_magic_data) pg_attribute_noreturn();
 static void check_restricted_library_name(const char *name);
@@ -112,7 +112,7 @@ load_external_function(const char *filename, const char *funcname,
 	fullname = expand_dynamic_library_name(filename);
 
 	/* Load the shared library, unless we already did */
-	lib_handle = internal_load_library(fullname);
+	lib_handle = internal_load_library(fullname, NULL);
 
 	/* Return handle if caller wants it */
 	if (filehandle)
@@ -141,6 +141,15 @@ load_external_function(const char *filename, const char *funcname,
  */
 void
 load_file(const char *filename, bool restricted)
+{
+	load_file_guc(filename, restricted, NULL);
+}
+
+/*
+ * Also accepts a GUC arg, for error reports
+ */
+void
+load_file_guc(const char *filename, bool restricted, const char *gucname)
 {
 	char	   *fullname;
 
@@ -152,7 +161,7 @@ load_file(const char *filename, bool restricted)
 	fullname = expand_dynamic_library_name(filename);
 
 	/* Load the shared library */
-	(void) internal_load_library(fullname);
+	(void) internal_load_library(fullname, gucname);
 
 	pfree(fullname);
 }
@@ -171,6 +180,7 @@ lookup_external_function(void *filehandle, const char *funcname)
 /*
  * Load the specified dynamic-link library file, unless it already is
  * loaded.  Return the pg_dl* handle for the file.
+ * gucname may be passed for error reports.
  *
  * Note: libname is expected to be an exact name for the library file.
  *
@@ -180,7 +190,7 @@ lookup_external_function(void *filehandle, const char *funcname)
  * perhaps other things that are definitely unsafe currently.
  */
 static void *
-internal_load_library(const char *libname)
+internal_load_library(const char *libname, const char *gucname)
 {
 	DynamicFileList *file_scanner;
 	PGModuleMagicFunction magic_func;
@@ -205,6 +215,7 @@ internal_load_library(const char *libname)
 		if (stat(libname, &stat_buf) == -1)
 			ereport(ERROR,
 					(errcode_for_file_access(),
+					 gucname ? errcontext("while loading shared libraries for setting \"%s\"", gucname) : 0,
 					 errmsg("could not access file \"%s\": %m",
 							libname)));
 
@@ -676,7 +687,7 @@ RestoreLibraryState(char *start_address)
 {
 	while (*start_address != '\0')
 	{
-		internal_load_library(start_address);
+		internal_load_library(start_address, NULL);
 		start_address += strlen(start_address) + 1;
 	}
 }
diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c
index 537d92c0cfd..8f11f718135 100644
--- a/src/backend/utils/init/miscinit.c
+++ b/src/backend/utils/init/miscinit.c
@@ -1825,7 +1825,7 @@ load_libraries(const char *libraries, const char *gucname, bool restricted)
 			expanded = psprintf("$libdir/plugins/%s", filename);
 			filename = expanded;
 		}
-		load_file(filename, restricted);
+		load_file_guc(filename, restricted, gucname);
 		ereport(DEBUG1,
 				(errmsg_internal("loaded library \"%s\"", filename)));
 		if (expanded)
diff --git a/src/include/fmgr.h b/src/include/fmgr.h
index c6319782a99..22e70dc43ea 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -745,6 +745,7 @@ extern void *load_external_function(const char *filename, const char *funcname,
 									bool signalNotFound, void **filehandle);
 extern void *lookup_external_function(void *filehandle, const char *funcname);
 extern void load_file(const char *filename, bool restricted);
+extern void load_file_guc(const char *filename, bool restricted, const char *gucname);
 extern void **find_rendezvous_variable(const char *varName);
 extern Size EstimateLibraryStateSpace(void);
 extern void SerializeLibraryState(Size maxsize, char *start_address);
-- 
2.42.0