pg_upgrade: Improve error messages

Make wording more accurate and add strerror() information.

Discussion: https://www.postgresql.org/message-id/24c8bd05-aed1-6301-919d-8acbabdb8c24@2ndquadrant.com

src/bin/pg_upgrade/exec.c

@@ -146,7 +146,7 @@ exec_prog(const char *log_file, const char *opt_log_file,
 #endif
 
 	if (log == NULL)
-		pg_fatal("could not write to log file \"%s\"\n", log_file);
+		pg_fatal("could not open log file \"%s\": %m\n", log_file);
 
 #ifdef WIN32
 	/* Are we printing "command:" before its output? */
@@ -201,7 +201,7 @@ exec_prog(const char *log_file, const char *opt_log_file,
 	 * log these commands to a third file, but that just adds complexity.
 	 */
 	if ((log = fopen(log_file, "a")) == NULL)
-		pg_fatal("could not write to log file \"%s\"\n", log_file);
+		pg_fatal("could not write to log file \"%s\": %m\n", log_file);
 	fprintf(log, "\n\n");
 	fclose(log);
 #endif

src/bin/pg_upgrade/option.c

@@ -217,7 +217,7 @@ parseCommandLine(int argc, char *argv[])
 	}
 
 	if ((log_opts.internal = fopen_priv(INTERNAL_LOG_FILE, "a")) == NULL)
-		pg_fatal("could not write to log file \"%s\"\n", INTERNAL_LOG_FILE);
+		pg_fatal("could not open log file \"%s\": %m\n", INTERNAL_LOG_FILE);
 
 	if (log_opts.verbose)
 		pg_log(PG_REPORT, "Running in verbose mode\n");
@@ -226,7 +226,7 @@ parseCommandLine(int argc, char *argv[])
 	for (filename = output_files; *filename != NULL; filename++)
 	{
 		if ((fp = fopen_priv(*filename, "a")) == NULL)
-			pg_fatal("could not write to log file \"%s\"\n", *filename);
+			pg_fatal("could not write to log file \"%s\": %m\n", *filename);
 
 		/* Start with newline because we might be appending to a file. */
 		fprintf(fp, "\n"