On Sun, Jan 09, 2022 at 11:58:18AM -0800, Maciek Sakrejda wrote:
> On Sat, Jan 8, 2022 at 2:07 PM Justin Pryzby <pry...@telsasoft.com> wrote:
> > Unfortunately, the output for dlopen() is not portable, which (I think) 
> > means
> > most of what I wrote can't be made to work..  Since it doesn't work to call
> > dlopen() when using SET, I tried using just stat().  But that also fails on
> > windows, since one of the regression tests has an invalid filename involving
> > unbalanced quotes, which cause it to return EINVAL rather than ENOENT.  So 
> > SET
> > cannot warn portably, unless it includes no details at all (or we specially
> > handle the windows case), or change the pre-existing regression test.  But
> > there's a 2nd instability, too, apparently having to do with timing.  So I'm
> > planning to drop the 0001 patch.
> 
> Hmm. I think 001 is a big part of the usability improvement here.

I agree - it helps people avoid causing a disruption, rather than just helping
them to fix it faster.

> Could we not at least warn generically, without relaying the
> underlying error? The notable thing in this situation is that the
> specified library could not be loaded (and that it will almost
> certainly cause problems on restart). The specific error would be nice
> to have, but it's less important. What is the timing instability?

I saw regression diffs like this, showing that the warning could be displayed
before or after the SELECT was echoed.

https://cirrus-ci.com/task/6301672321318912
    -SELECT * FROM schema4.counted;
     WARNING:  could not load library: $libdir/plugins/worker_spi: cannot open 
shared object file: No such file or directory
    +SELECT * FROM schema4.counted;

It's certainly possible to show a static message without additional text from
errno.

On Tue, Dec 28, 2021 at 9:45 AM Justin Pryzby <pry...@telsasoft.com> wrote:
> > > For whatever reason, I get slightly different (and somewhat redundant)
> > > output on failing to start:
> > >
> > > 2022-01-08 12:59:36.784 PST [324482] WARNING:  could not load library: 
> > > $libdir/plugins/totally bogus: cannot open shared object file: No such 
> > > file or directory
> > > 2022-01-08 12:59:36.787 PST [324482] FATAL:  could not load library: 
> > > totally bogus: cannot open shared object file: No such file or directory
> > > 2022-01-08 12:59:36.787 PST [324482] LOG:  database system is shut down
> >
> > I think the first WARNING is from the GUC mechanism "setting" the library.
> > And then the FATAL is from trying to apply the GUC.
> > It looks like you didn't apply the 0002 patch for that test so got no 
> > CONTEXT ?
> 
> I still had the terminal open where I tested this, and the scrollback
> did show me applying the patch (and building after). I tried a make
> clean and applying the patch again, and I do see the CONTEXT line now.
> I'm not sure what the problem was but seems like PEBKAC--sorry about
> that.

Maybe you missed "make install" or similar.

I took the liberty of adding you as a reviewer here:
https://commitfest.postgresql.org/36/3482/

-- 
Justin
>From 53bf0c82ea76a00fbf1c95c4833f1bd302228d25 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryz...@telsasoft.com>
Date: Sat, 18 Dec 2021 22:51:01 -0600
Subject: [PATCH v3 1/2] errcontext if server fails to start due to library
 GUCs

---
 src/backend/utils/fmgr/dfmgr.c    | 20 +++++++++++++++-----
 src/backend/utils/init/miscinit.c |  2 +-
 src/include/fmgr.h                |  1 +
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/backend/utils/fmgr/dfmgr.c b/src/backend/utils/fmgr/dfmgr.c
index 050da780804..40eed5b5530 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 internal_unload_library(const char *libname);
@@ -115,7 +115,7 @@ 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)
@@ -144,6 +144,14 @@ 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;
 
@@ -158,7 +166,7 @@ load_file(const char *filename, bool restricted)
 	internal_unload_library(fullname);
 
 	/* Load the shared library */
-	(void) internal_load_library(fullname);
+	(void) internal_load_library(fullname, gucname);
 
 	pfree(fullname);
 }
@@ -179,9 +187,10 @@ lookup_external_function(void *filehandle, const char *funcname)
  * loaded.  Return the pg_dl* handle for the file.
  *
  * Note: libname is expected to be an exact name for the library file.
+ * gucname may be passed for error reports.
  */
 static void *
-internal_load_library(const char *libname)
+internal_load_library(const char *libname, const char *gucname)
 {
 	DynamicFileList *file_scanner;
 	PGModuleMagicFunction magic_func;
@@ -206,6 +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 GUC \"%s\"", gucname) : 0,
 					 errmsg("could not access file \"%s\": %m",
 							libname)));
 
@@ -764,7 +774,7 @@ 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 0f2570d6264..5c295e44ff8 100644
--- a/src/backend/utils/init/miscinit.c
+++ b/src/backend/utils/init/miscinit.c
@@ -1658,7 +1658,7 @@ 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 6560e462d66..9dccd0fc047 100644
--- a/src/include/fmgr.h
+++ b/src/include/fmgr.h
@@ -727,6 +727,7 @@ 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);
-- 
2.17.1

>From 76f2caade9c0e3554ecb645c99ad148e593a9fe6 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryz...@telsasoft.com>
Date: Mon, 13 Dec 2021 08:42:38 -0600
Subject: [PATCH v3 2/2] warn when setting GUC to a nonextant library

XXX: the SPI test is unstable:

-SELECT * FROM schema4.counted;
 WARNING:  could not load library: $libdir/plugins/worker_spi: cannot open shared object file: No such file or directory
+SELECT * FROM schema4.counted;
---
 src/backend/utils/misc/guc.c                  | 85 ++++++++++++++++++-
 .../unsafe_tests/expected/rolenames.out       |  1 +
 .../worker_spi/expected/worker_spi.out        |  2 +
 .../modules/worker_spi/sql/worker_spi.sql     |  2 +
 src/test/regress/expected/rules.out           |  5 ++
 src/test/regress/sql/rules.sql                |  1 +
 6 files changed, 93 insertions(+), 3 deletions(-)

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 4c94f09c645..5a228a37ee2 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -170,6 +170,12 @@ static bool call_enum_check_hook(struct config_enum *conf, int *newval,
 								 void **extra, GucSource source, int elevel);
 
 static bool check_log_destination(char **newval, void **extra, GucSource source);
+static bool check_local_preload_libraries(char **newval, void **extra,
+		GucSource source);
+static bool check_session_preload_libraries(char **newval, void **extra,
+		GucSource source);
+static bool check_shared_preload_libraries(char **newval, void **extra,
+		GucSource source);
 static void assign_log_destination(const char *newval, void *extra);
 
 static bool check_wal_consistency_checking(char **newval, void **extra,
@@ -4188,7 +4194,7 @@ static struct config_string ConfigureNamesString[] =
 		},
 		&session_preload_libraries_string,
 		"",
-		NULL, NULL, NULL
+		check_session_preload_libraries, NULL, NULL
 	},
 
 	{
@@ -4199,7 +4205,7 @@ static struct config_string ConfigureNamesString[] =
 		},
 		&shared_preload_libraries_string,
 		"",
-		NULL, NULL, NULL
+		check_shared_preload_libraries, NULL, NULL
 	},
 
 	{
@@ -4210,7 +4216,7 @@ static struct config_string ConfigureNamesString[] =
 		},
 		&local_preload_libraries_string,
 		"",
-		NULL, NULL, NULL
+		check_local_preload_libraries, NULL, NULL
 	},
 
 	{
@@ -12100,6 +12106,79 @@ check_max_worker_processes(int *newval, void **extra, GucSource source)
 	return true;
 }
 
+/*
+ * See also load_libraries() and internal_load_library().
+ */
+static bool
+check_preload_libraries(char **newval, void **extra, GucSource source,
+	bool restricted)
+{
+	char		*rawstring;
+	List		*elemlist;
+	ListCell	*l;
+
+	/* nothing to do if empty */
+	if (newval == NULL || *newval[0] == '\0')
+		return true;
+
+	/* Need a modifiable copy of string */
+	rawstring = pstrdup(*newval);
+
+	/* Parse string into list of filename paths */
+	if (!SplitDirectoriesString(rawstring, ',', &elemlist))
+	{
+		/* Should not happen ? */
+		return false;
+	}
+
+	foreach(l, elemlist)
+	{
+		/* Note that filename was already canonicalized */
+		char       *filename = (char *) lfirst(l);
+		char       *expanded = NULL;
+
+		/* If restricting, insert $libdir/plugins if not mentioned already */
+		if (restricted && first_dir_separator(filename) == NULL)
+		{
+			expanded = psprintf("$libdir/plugins/%s", filename);
+			filename = expanded;
+		}
+
+		/*
+		 * stat()/access() only check that the library exists, not that it has
+		 * the correct magic number or even a library.  But error messages from
+		 * dlopen() are not portable, so it'd be hard to report any problem
+		 * other than "does not exist".
+		 */
+		if (access(filename, R_OK) == -1) // F_OK
+			ereport(WARNING,
+					errcode_for_file_access(),
+					 errmsg("could not access file \"%s\"", filename));
+	}
+
+	list_free_deep(elemlist);
+	pfree(rawstring);
+	return true;
+}
+
+static bool
+check_shared_preload_libraries(char **newval, void **extra, GucSource source)
+{
+	return check_preload_libraries(newval, extra, source, true);
+}
+
+static bool
+check_local_preload_libraries(char **newval, void **extra, GucSource source)
+{
+	return check_preload_libraries(newval, extra, source, false);
+}
+
+static bool
+check_session_preload_libraries(char **newval, void **extra, GucSource source)
+{
+	return check_preload_libraries(newval, extra, source, true);
+}
+
 static bool
 check_effective_io_concurrency(int *newval, void **extra, GucSource source)
 {
diff --git a/src/test/modules/unsafe_tests/expected/rolenames.out b/src/test/modules/unsafe_tests/expected/rolenames.out
index eb608fdc2ea..368b10558d7 100644
--- a/src/test/modules/unsafe_tests/expected/rolenames.out
+++ b/src/test/modules/unsafe_tests/expected/rolenames.out
@@ -1066,6 +1066,7 @@ GRANT pg_read_all_settings TO regress_role_haspriv;
 BEGIN;
 -- A GUC using GUC_SUPERUSER_ONLY is useful for negative tests.
 SET LOCAL session_preload_libraries TO 'path-to-preload-libraries';
+WARNING:  could not access file "$libdir/plugins/path-to-preload-libraries"
 SET SESSION AUTHORIZATION regress_role_haspriv;
 -- passes with role member of pg_read_all_settings
 SHOW session_preload_libraries;
diff --git a/src/test/modules/worker_spi/expected/worker_spi.out b/src/test/modules/worker_spi/expected/worker_spi.out
index dc0a79bf759..5b275669bcf 100644
--- a/src/test/modules/worker_spi/expected/worker_spi.out
+++ b/src/test/modules/worker_spi/expected/worker_spi.out
@@ -28,6 +28,8 @@ SELECT pg_reload_conf();
  t
 (1 row)
 
+-- reconnect to avoid unstable test result due to asynchronous signal
+\c
 -- wait until the worker has processed the tuple we just inserted
 DO $$
 DECLARE
diff --git a/src/test/modules/worker_spi/sql/worker_spi.sql b/src/test/modules/worker_spi/sql/worker_spi.sql
index 4683523b29d..4ed5370d456 100644
--- a/src/test/modules/worker_spi/sql/worker_spi.sql
+++ b/src/test/modules/worker_spi/sql/worker_spi.sql
@@ -18,6 +18,8 @@ END
 $$;
 INSERT INTO schema4.counted VALUES ('total', 0), ('delta', 1);
 SELECT pg_reload_conf();
+-- reconnect to avoid unstable test result due to asynchronous signal
+\c
 -- wait until the worker has processed the tuple we just inserted
 DO $$
 DECLARE
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index d652f7b5fb4..ce396814332 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -3574,6 +3574,7 @@ drop table hats;
 drop table hat_data;
 -- test for pg_get_functiondef properly regurgitating SET parameters
 -- Note that the function is kept around to stress pg_dump.
+SET check_function_bodies=no;
 CREATE FUNCTION func_with_set_params() RETURNS integer
     AS 'select 1;'
     LANGUAGE SQL
@@ -3583,6 +3584,10 @@ CREATE FUNCTION func_with_set_params() RETURNS integer
     SET datestyle to iso, mdy
     SET local_preload_libraries TO "Mixed/Case", 'c:/''a"/path', '', '0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789'
     IMMUTABLE STRICT;
+WARNING:  could not access file "Mixed/Case"
+WARNING:  could not access file "c:/'a"/path"
+WARNING:  could not access file ""
+WARNING:  could not access file "0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"
 SELECT pg_get_functiondef('func_with_set_params()'::regprocedure);
                                                                             pg_get_functiondef                                                                            
 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------
diff --git a/src/test/regress/sql/rules.sql b/src/test/regress/sql/rules.sql
index b732833e63c..1e42d092862 100644
--- a/src/test/regress/sql/rules.sql
+++ b/src/test/regress/sql/rules.sql
@@ -1198,6 +1198,7 @@ drop table hat_data;
 
 -- test for pg_get_functiondef properly regurgitating SET parameters
 -- Note that the function is kept around to stress pg_dump.
+SET check_function_bodies=no;
 CREATE FUNCTION func_with_set_params() RETURNS integer
     AS 'select 1;'
     LANGUAGE SQL
-- 
2.17.1

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