Use printf's %m format instead of strerror(errno) in more places

Most callers of strerror() are removed from the backend code.  The
remaining callers require special handling with a saved errno from a
previous system call.  The frontend code still needs strerror() where
error states need to be handled outside of fprintf.

Note that pg_regress is not changed to use %m as the TAP output may
clobber errno, since those functions call fprintf() and friends before
evaluating the format string.

Support for %m in src/port/snprintf.c has been added in d6c55de,
hence all the stable branches currently supported include it.

Author: Dagfinn Ilmari Mannsåker
Discussion: https://postgr.es/m/87sf13jhuw.fsf@wibble.ilmari.org

Author: michaelpq

src/backend/postmaster/postmaster.c

@@ -1375,12 +1375,12 @@ PostmasterMain(int argc, char *argv[])
 
 			/* Make PID file world readable */
 			if (chmod(external_pid_file, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) != 0)
-				write_stderr("%s: could not change permissions of external PID file \"%s\": %s\n",
-							 progname, external_pid_file, strerror(errno));
+				write_stderr("%s: could not change permissions of external PID file \"%s\": %m\n",
+							 progname, external_pid_file);
 		}
 		else
-			write_stderr("%s: could not write external PID file \"%s\": %s\n",
-						 progname, external_pid_file, strerror(errno));
+			write_stderr("%s: could not write external PID file \"%s\": %m\n",
+						 progname, external_pid_file);
 
 		on_proc_exit(unlink_external_pid_file, 0);
 	}
@@ -1589,8 +1589,8 @@ checkControlFile(void)
 	{
 		write_stderr("%s: could not find the database system\n"
 					 "Expected to find it in the directory \"%s\",\n"
-					 "but could not open file \"%s\": %s\n",
-					 progname, DataDir, path, strerror(errno));
+					 "but could not open file \"%s\": %m\n",
+					 progname, DataDir, path);
 		ExitPostmaster(2);
 	}
 	FreeFile(fp);
@@ -6277,24 +6277,21 @@ read_backend_variables(char *id, Port **port, BackgroundWorker **worker)
 	fp = AllocateFile(id, PG_BINARY_R);
 	if (!fp)
 	{
-		write_stderr("could not open backend variables file \"%s\": %s\n",
-					 id, strerror(errno));
+		write_stderr("could not open backend variables file \"%s\": %m\n", id);
 		exit(1);
 	}
 
 	if (fread(&param, sizeof(param), 1, fp) != 1)
 	{
-		write_stderr("could not read from backend variables file \"%s\": %s\n",
-					 id, strerror(errno));
+		write_stderr("could not read from backend variables file \"%s\": %m\n", id);
 		exit(1);
 	}
 
 	/* Release file */
 	FreeFile(fp);
 	if (unlink(id) != 0)
 	{
-		write_stderr("could not remove file \"%s\": %s\n",
-					 id, strerror(errno));
+		write_stderr("could not remove file \"%s\": %m\n", id);
 		exit(1);
 	}
 #else

src/backend/postmaster/syslogger.c

@@ -1173,7 +1173,7 @@ write_syslogger_file(const char *buffer, int count, int destination)
 	 * to our input pipe which would result in a different sort of looping.
 	 */
 	if (rc != count)
-		write_stderr("could not write to log file: %s\n", strerror(errno));
+		write_stderr("could not write to log file: %m\n");
 }
 
 #ifdef WIN32

src/backend/utils/misc/guc.c

@@ -1799,10 +1799,9 @@ SelectConfigFiles(const char *userDoption, const char *progname)
 
 	if (configdir && stat(configdir, &stat_buf) != 0)
 	{
-		write_stderr("%s: could not access directory \"%s\": %s\n",
+		write_stderr("%s: could not access directory \"%s\": %m\n",
 					 progname,
-					 configdir,
-					 strerror(errno));
+					 configdir);
 		if (errno == ENOENT)
 			write_stderr("Run initdb or pg_basebackup to initialize a PostgreSQL data directory.\n");
 		return false;
@@ -1851,8 +1850,8 @@ SelectConfigFiles(const char *userDoption, const char *progname)
 	 */
 	if (stat(ConfigFileName, &stat_buf) != 0)
 	{
-		write_stderr("%s: could not access the server configuration file \"%s\": %s\n",
-					 progname, ConfigFileName, strerror(errno));
+		write_stderr("%s: could not access the server configuration file \"%s\": %m\n",
+					 progname, ConfigFileName);
 		free(configdir);
 		return false;
 	}

src/bin/initdb/findtimezone.c

@@ -680,8 +680,8 @@ scan_available_timezones(char *tzdir, char *tzdirsub, struct tztry *tt,
 		if (stat(tzdir, &statbuf) != 0)
 		{
 #ifdef DEBUG_IDENTIFY_TIMEZONE
-			fprintf(stderr, "could not stat \"%s\": %s\n",
-					tzdir, strerror(errno));
+			fprintf(stderr, "could not stat \"%s\": %m\n",
+					tzdir);
 #endif
 			tzdir[tzdir_orig_len] = '\0';
 			continue;

src/bin/pg_ctl/pg_ctl.c

@@ -254,8 +254,8 @@ get_pgpid(bool is_status_request)
 			write_stderr(_("%s: directory \"%s\" does not exist\n"), progname,
 						 pg_data);
 		else
-			write_stderr(_("%s: could not access directory \"%s\": %s\n"), progname,
-						 pg_data, strerror(errno));
+			write_stderr(_("%s: could not access directory \"%s\": %m\n"), progname,
+						 pg_data);
 
 		/*
 		 * The Linux Standard Base Core Specification 3.1 says this should
@@ -280,8 +280,8 @@ get_pgpid(bool is_status_request)
 			return 0;
 		else
 		{
-			write_stderr(_("%s: could not open PID file \"%s\": %s\n"),
-						 progname, pid_file, strerror(errno));
+			write_stderr(_("%s: could not open PID file \"%s\": %m\n"),
+						 progname, pid_file);
 			exit(1);
 		}
 	}
@@ -454,8 +454,8 @@ start_postmaster(void)
 	if (pm_pid < 0)
 	{
 		/* fork failed */
-		write_stderr(_("%s: could not start server: %s\n"),
-					 progname, strerror(errno));
+		write_stderr(_("%s: could not start server: %m\n"),
+					 progname);
 		exit(1);
 	}
 	if (pm_pid > 0)
@@ -474,8 +474,8 @@ start_postmaster(void)
 #ifdef HAVE_SETSID
 	if (setsid() < 0)
 	{
-		write_stderr(_("%s: could not start server due to setsid() failure: %s\n"),
-					 progname, strerror(errno));
+		write_stderr(_("%s: could not start server due to setsid() failure: %m\n"),
+					 progname);
 		exit(1);
 	}
 #endif
@@ -496,8 +496,8 @@ start_postmaster(void)
 	(void) execl("/bin/sh", "/bin/sh", "-c", cmd, (char *) NULL);
 
 	/* exec failed */
-	write_stderr(_("%s: could not start server: %s\n"),
-				 progname, strerror(errno));
+	write_stderr(_("%s: could not start server: %m\n"),
+				 progname);
 	exit(1);
 
 	return 0;					/* keep dumb compilers quiet */
@@ -544,8 +544,8 @@ start_postmaster(void)
 			 */
 			if (errno != ENOENT)
 			{
-				write_stderr(_("%s: could not open log file \"%s\": %s\n"),
-							 progname, log_file, strerror(errno));
+				write_stderr(_("%s: could not open log file \"%s\": %m\n"),
+							 progname, log_file);
 				exit(1);
 			}
 		}
@@ -851,8 +851,8 @@ trap_sigint_during_startup(SIGNAL_ARGS)
 	if (postmasterPID != -1)
 	{
 		if (kill(postmasterPID, SIGINT) != 0)
-			write_stderr(_("%s: could not send stop signal (PID: %d): %s\n"),
-						 progname, (int) postmasterPID, strerror(errno));
+			write_stderr(_("%s: could not send stop signal (PID: %d): %m\n"),
+						 progname, (int) postmasterPID);
 	}
 
 	/*
@@ -1035,8 +1035,7 @@ do_stop(void)
 
 	if (kill(pid, sig) != 0)
 	{
-		write_stderr(_("%s: could not send stop signal (PID: %d): %s\n"), progname, (int) pid,
-					 strerror(errno));
+		write_stderr(_("%s: could not send stop signal (PID: %d): %m\n"), progname, (int) pid);
 		exit(1);
 	}
 
@@ -1103,8 +1102,7 @@ do_restart(void)
 	{
 		if (kill(pid, sig) != 0)
 		{
-			write_stderr(_("%s: could not send stop signal (PID: %d): %s\n"), progname, (int) pid,
-						 strerror(errno));
+			write_stderr(_("%s: could not send stop signal (PID: %d): %m\n"), progname, (int) pid);
 			exit(1);
 		}
 
@@ -1159,8 +1157,8 @@ do_reload(void)
 
 	if (kill(pid, sig) != 0)
 	{
-		write_stderr(_("%s: could not send reload signal (PID: %d): %s\n"),
-					 progname, (int) pid, strerror(errno));
+		write_stderr(_("%s: could not send reload signal (PID: %d): %m\n"),
+					 progname, (int) pid);
 		exit(1);
 	}
 
@@ -1207,25 +1205,25 @@ do_promote(void)
 
 	if ((prmfile = fopen(promote_file, "w")) == NULL)
 	{
-		write_stderr(_("%s: could not create promote signal file \"%s\": %s\n"),
-					 progname, promote_file, strerror(errno));
+		write_stderr(_("%s: could not create promote signal file \"%s\": %m\n"),
+					 progname, promote_file);
 		exit(1);
 	}
 	if (fclose(prmfile))
 	{
-		write_stderr(_("%s: could not write promote signal file \"%s\": %s\n"),
-					 progname, promote_file, strerror(errno));
+		write_stderr(_("%s: could not write promote signal file \"%s\": %m\n"),
+					 progname, promote_file);
 		exit(1);
 	}
 
 	sig = SIGUSR1;
 	if (kill(pid, sig) != 0)
 	{
-		write_stderr(_("%s: could not send promote signal (PID: %d): %s\n"),
-					 progname, (int) pid, strerror(errno));
+		write_stderr(_("%s: could not send promote signal (PID: %d): %m\n"),
+					 progname, (int) pid);
 		if (unlink(promote_file) != 0)
-			write_stderr(_("%s: could not remove promote signal file \"%s\": %s\n"),
-						 progname, promote_file, strerror(errno));
+			write_stderr(_("%s: could not remove promote signal file \"%s\": %m\n"),
+						 progname, promote_file);
 		exit(1);
 	}
 
@@ -1280,25 +1278,25 @@ do_logrotate(void)
 
 	if ((logrotatefile = fopen(logrotate_file, "w")) == NULL)
 	{
-		write_stderr(_("%s: could not create log rotation signal file \"%s\": %s\n"),
-					 progname, logrotate_file, strerror(errno));
+		write_stderr(_("%s: could not create log rotation signal file \"%s\": %m\n"),
+					 progname, logrotate_file);
 		exit(1);
 	}
 	if (fclose(logrotatefile))
 	{
-		write_stderr(_("%s: could not write log rotation signal file \"%s\": %s\n"),
-					 progname, logrotate_file, strerror(errno));
+		write_stderr(_("%s: could not write log rotation signal file \"%s\": %m\n"),
+					 progname, logrotate_file);
 		exit(1);
 	}
 
 	sig = SIGUSR1;
 	if (kill(pid, sig) != 0)
 	{
-		write_stderr(_("%s: could not send log rotation signal (PID: %d): %s\n"),
-					 progname, (int) pid, strerror(errno));
+		write_stderr(_("%s: could not send log rotation signal (PID: %d): %m\n"),
+					 progname, (int) pid);
 		if (unlink(logrotate_file) != 0)
-			write_stderr(_("%s: could not remove log rotation signal file \"%s\": %s\n"),
-						 progname, logrotate_file, strerror(errno));
+			write_stderr(_("%s: could not remove log rotation signal file \"%s\": %m\n"),
+						 progname, logrotate_file);
 		exit(1);
 	}
 
@@ -1396,8 +1394,8 @@ do_kill(pid_t pid)
 {
 	if (kill(pid, sig) != 0)
 	{
-		write_stderr(_("%s: could not send signal %d (PID: %d): %s\n"),
-					 progname, sig, (int) pid, strerror(errno));
+		write_stderr(_("%s: could not send signal %d (PID: %d): %m\n"),
+					 progname, sig, (int) pid);
 		exit(1);
 	}
 }

src/bin/pg_dump/compress_gzip.c

@@ -292,7 +292,7 @@ Gzip_getc(CompressFileHandle *CFH)
 	if (ret == EOF)
 	{
 		if (!gzeof(gzfp))
-			pg_fatal("could not read from input file: %s", strerror(errno));
+			pg_fatal("could not read from input file: %m");
 		else
 			pg_fatal("could not read from input file: end of file");
 	}

src/bin/pg_dump/compress_none.c

@@ -94,8 +94,7 @@ read_none(void *ptr, size_t size, size_t *rsize, CompressFileHandle *CFH)
 
 	ret = fread(ptr, 1, size, fp);
 	if (ret != size && !feof(fp))
-		pg_fatal("could not read from input file: %s",
-				 strerror(errno));
+		pg_fatal("could not read from input file: %m");
 
 	if (rsize)
 		*rsize = ret;
@@ -137,7 +136,7 @@ getc_none(CompressFileHandle *CFH)
 	if (ret == EOF)
 	{
 		if (!feof(fp))
-			pg_fatal("could not read from input file: %s", strerror(errno));
+			pg_fatal("could not read from input file: %m");
 		else
 			pg_fatal("could not read from input file: end of file");
 	}