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 d6c55de1f99a,
hence all the stable branches currently supported include it.

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

3 files changed, 14 insertions, 18 deletions

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index f3c09e8dc0d..af8a1efe665 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/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);
@@ -6277,15 +6277,13 @@ 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);
 	}
 
@@ -6293,8 +6291,7 @@ read_backend_variables(char *id, Port **port, BackgroundWorker **worker)
 	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
diff --git a/src/backend/postmaster/syslogger.c b/src/backend/postmaster/syslogger.c
index c2a6a226e70..d9d042f5628 100644
--- a/src/backend/postmaster/syslogger.c
+++ b/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
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index dd5a46469a6..391866145ee 100644
--- a/src/backend/utils/misc/guc.c
+++ b/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;
 	}