Suppress -Wunused-result warnings about write() and fwrite().

This is merely an exercise in satisfying pedants, not a bug fix, because
in every case we were checking for failure later with ferror(), or else
there was nothing useful to be done about a failure anyway.  Document
the latter cases.

Author: tglsfdc

src/backend/access/transam/xlog.c

@@ -9067,8 +9067,10 @@ do_pg_start_backup(const char *backupidstr, bool fast, char **labelfile)
 						(errcode_for_file_access(),
 						 errmsg("could not create file \"%s\": %m",
 								BACKUP_LABEL_FILE)));
-			fwrite(labelfbuf.data, labelfbuf.len, 1, fp);
-			if (fflush(fp) || ferror(fp) || FreeFile(fp))
+			if (fwrite(labelfbuf.data, labelfbuf.len, 1, fp) != 1 ||
+				fflush(fp) != 0 ||
+				ferror(fp) ||
+				FreeFile(fp))
 				ereport(ERROR,
 						(errcode_for_file_access(),
 						 errmsg("could not write file \"%s\": %m",

src/backend/commands/copy.c

@@ -466,9 +466,9 @@ CopySendEndOfRow(CopyState cstate)
 #endif
 			}
 
-			(void) fwrite(fe_msgbuf->data, fe_msgbuf->len,
-						  1, cstate->copy_file);
-			if (ferror(cstate->copy_file))
+			if (fwrite(fe_msgbuf->data, fe_msgbuf->len, 1,
+					   cstate->copy_file) != 1 ||
+				ferror(cstate->copy_file))
 				ereport(ERROR,
 						(errcode_for_file_access(),
 						 errmsg("could not write to COPY file: %m")));

src/backend/postmaster/pgstat.c

@@ -3284,6 +3284,7 @@ pgstat_write_statsfile(bool permanent)
 	int32		format_id;
 	const char *tmpfile = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
 	const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
+	int			rc;
 
 	/*
 	 * Open the statistics temp file to write out the current values.
@@ -3307,12 +3308,14 @@ pgstat_write_statsfile(bool permanent)
 	 * Write the file header --- currently just a format ID.
 	 */
 	format_id = PGSTAT_FILE_FORMAT_ID;
-	fwrite(&format_id, sizeof(format_id), 1, fpout);
+	rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
+	(void) rc;					/* we'll check for error with ferror */
 
 	/*
 	 * Write global stats struct
 	 */
-	fwrite(&globalStats, sizeof(globalStats), 1, fpout);
+	rc = fwrite(&globalStats, sizeof(globalStats), 1, fpout);
+	(void) rc;					/* we'll check for error with ferror */
 
 	/*
 	 * Walk through the database table.
@@ -3326,7 +3329,8 @@ pgstat_write_statsfile(bool permanent)
 		 * use to any other process.
 		 */
 		fputc('D', fpout);
-		fwrite(dbentry, offsetof(PgStat_StatDBEntry, tables), 1, fpout);
+		rc = fwrite(dbentry, offsetof(PgStat_StatDBEntry, tables), 1, fpout);
+		(void) rc;				/* we'll check for error with ferror */
 
 		/*
 		 * Walk through the database's access stats per table.
@@ -3335,7 +3339,8 @@ pgstat_write_statsfile(bool permanent)
 		while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
 		{
 			fputc('T', fpout);
-			fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
+			rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
+			(void) rc;			/* we'll check for error with ferror */
 		}
 
 		/*
@@ -3345,7 +3350,8 @@ pgstat_write_statsfile(bool permanent)
 		while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
 		{
 			fputc('F', fpout);
-			fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
+			rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
+			(void) rc;			/* we'll check for error with ferror */
 		}
 
 		/*

src/backend/utils/error/elog.c

@@ -1747,10 +1747,12 @@ write_eventlog(int level, const char *line, int len)
 static void
 write_console(const char *line, int len)
 {
+	int			rc;
+
 #ifdef WIN32
 
 	/*
-	 * WriteConsoleW() will fail of stdout is redirected, so just fall through
+	 * WriteConsoleW() will fail if stdout is redirected, so just fall through
 	 * to writing unconverted to the logfile in this case.
 	 *
 	 * Since we palloc the structure required for conversion, also fall
@@ -1788,13 +1790,18 @@ write_console(const char *line, int len)
 #else
 
 	/*
-	 * Conversion on non-win32 platform is not implemented yet. It requires
+	 * Conversion on non-win32 platforms is not implemented yet. It requires
 	 * non-throw version of pg_do_encoding_conversion(), that converts
 	 * unconvertable characters to '?' without errors.
 	 */
 #endif
 
-	write(fileno(stderr), line, len);
+	/*
+	 * We ignore any error from write() here.  We have no useful way to report
+	 * it ... certainly whining on stderr isn't likely to be productive.
+	 */
+	rc = write(fileno(stderr), line, len);
+	(void) rc;
 }
 
 /*
@@ -2457,13 +2464,30 @@ send_message_to_server_log(ErrorData *edata)
 
 /*
  * Send data to the syslogger using the chunked protocol
+ *
+ * Note: when there are multiple backends writing into the syslogger pipe,
+ * it's critical that each write go into the pipe indivisibly, and not
+ * get interleaved with data from other processes.  Fortunately, the POSIX
+ * spec requires that writes to pipes be atomic so long as they are not
+ * more than PIPE_BUF bytes long.  So we divide long messages into chunks
+ * that are no more than that length, and send one chunk per write() call.
+ * The collector process knows how to reassemble the chunks.
+ *
+ * Because of the atomic write requirement, there are only two possible
+ * results from write() here: -1 for failure, or the requested number of
+ * bytes.  There is not really anything we can do about a failure; retry would
+ * probably be an infinite loop, and we can't even report the error usefully.
+ * (There is noplace else we could send it!)  So we might as well just ignore
+ * the result from write().  However, on some platforms you get a compiler
+ * warning from ignoring write()'s result, so do a little dance with casting
+ * rc to void to shut up the compiler.
  */
 static void
 write_pipe_chunks(char *data, int len, int dest)
 {
 	PipeProtoChunk p;
-
 	int			fd = fileno(stderr);
+	int			rc;
 
 	Assert(len > 0);
 
@@ -2476,7 +2500,8 @@ write_pipe_chunks(char *data, int len, int dest)
 		p.proto.is_last = (dest == LOG_DESTINATION_CSVLOG ? 'F' : 'f');
 		p.proto.len = PIPE_MAX_PAYLOAD;
 		memcpy(p.proto.data, data, PIPE_MAX_PAYLOAD);
-		write(fd, &p, PIPE_HEADER_SIZE + PIPE_MAX_PAYLOAD);
+		rc = write(fd, &p, PIPE_HEADER_SIZE + PIPE_MAX_PAYLOAD);
+		(void) rc;
 		data += PIPE_MAX_PAYLOAD;
 		len -= PIPE_MAX_PAYLOAD;
 	}
@@ -2485,7 +2510,8 @@ write_pipe_chunks(char *data, int len, int dest)
 	p.proto.is_last = (dest == LOG_DESTINATION_CSVLOG ? 'T' : 't');
 	p.proto.len = len;
 	memcpy(p.proto.data, data, len);
-	write(fd, &p, PIPE_HEADER_SIZE + len);
+	rc = write(fd, &p, PIPE_HEADER_SIZE + len);
+	(void) rc;
 }
 
 

src/bin/psql/common.c

@@ -228,6 +228,7 @@ static void
 handle_sigint(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
+	int			rc;
 	char		errbuf[256];
 
 	/* if we are waiting for input, longjmp out of it */
@@ -244,11 +245,16 @@ handle_sigint(SIGNAL_ARGS)
 	if (cancelConn != NULL)
 	{
 		if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
-			write_stderr("Cancel request sent\n");
+		{
+			rc = write_stderr("Cancel request sent\n");
+			(void) rc;			/* ignore errors, nothing we can do here */
+		}
 		else
 		{
-			write_stderr("Could not send cancel request: ");
-			write_stderr(errbuf);
+			rc = write_stderr("Could not send cancel request: ");
+			(void) rc;			/* ignore errors, nothing we can do here */
+			rc = write_stderr(errbuf);
+			(void) rc;			/* ignore errors, nothing we can do here */
 		}
 	}