8000 Suppress -Wunused-result warnings about write() and fwrite(). · fschopp/postgres@aa90e14 · GitHub
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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.
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5 files changed

+59
-19
lines changed

5 files changed

+59
-19
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -9067,8 +9067,10 @@ do_pg_start_backup(const char *backupidstr, bool fast, char **labelfile)
90679067
(errcode_for_file_access(),
90689068
errmsg("could not create file \"%s\": %m",
90699069
BACKUP_LABEL_FILE)));
9070-
fwrite(labelfbuf.data, labelfbuf.len, 1, fp);
9071-
if (fflush(fp) || ferror(fp) || FreeFile(fp))
9070+
if (fwrite(labelfbuf.data, labelfbuf.len, 1, fp) != 1 ||
9071+
fflush(fp) != 0 ||
9072+
ferror(fp) ||
9073+
FreeFile(fp))
90729074
ereport(ERROR,
90739075
(errcode_for_file_access(),
90749076
errmsg("could not write file \"%s\": %m",

‎src/backend/commands/copy.c

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -466,9 +466,9 @@ CopySendEndOfRow(CopyState cstate)
466466
#endif
467467
}
468468

469-
(void) fwrite(fe_msgbuf->data, fe_msgbuf->len,
470-
1, cstate->copy_file);
471-
if (ferror(cstate->copy_file))
469+
if (fwrite(fe_msgbuf->data, fe_msgbuf->len, 1,
470+
cstate->copy_file) != 1 ||
471+
ferror(cstate->copy_file))
472472
ereport(ERROR,
473473
(errcode_for_file_access(),
474474
errmsg("could not write to COPY file: %m")));

‎src/backend/postmaster/pgstat.c

Lines changed: 11 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -3284,6 +3284,7 @@ pgstat_write_statsfile(bool permanent)
32843284
int32 format_id;
32853285
const char *tmpfile = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
32863286
const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
3287+
int rc;
32873288

32883289
/*
32893290
* Open the statistics temp file to write out the current values.
@@ -3307,12 +3308,14 @@ pgstat_write_statsfile(bool permanent)
33073308
* Write the file header --- currently just a format ID.
33083309
*/
33093310
format_id = PGSTAT_FILE_FORMAT_ID;
3310-
fwrite(&format_id, sizeof(format_id), 1, fpout);
3311+
rc = fwrite(&format_id, sizeof(format_id), 1, fpout);
3312+
(void) rc; /* we'll check for error with ferror */
33113313

33123314
/*
33133315
* Write global stats struct
33143316
*/
3315-
fwrite(&globalStats, sizeof(globalStats), 1, fpout);
3317+
rc = fwrite(&globalStats, sizeof(globalStats), 1, fpout);
3318+
(void) rc; /* we'll check for error with ferror */
33163319

33173320
/*
33183321
* Walk through the database table.
@@ -3326,7 +3329,8 @@ pgstat_write_statsfile(bool permanent)
33263329
* use to any other process.
33273330
*/
33283331
fputc('D', fpout);
3329-
fwrite(dbentry, offsetof(PgStat_StatDBEntry, tables), 1, fpout);
3332+
rc = fwrite(dbentry, offsetof(PgStat_StatDBEntry, tables), 1, fpout);
3333+
(void) rc; /* we'll check for error with ferror */
33303334

33313335
/*
33323336
* Walk through the database's access stats per table.
@@ -3335,7 +3339,8 @@ pgstat_write_statsfile(bool permanent)
33353339
while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
33363340
{
33373341
fputc('T', fpout);
3338-
fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
3342+
rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
3343+
(void) rc; /* we'll check for error with ferror */
33393344
}
33403345

33413346
/*
@@ -3345,7 +3350,8 @@ pgstat_write_statsfile(bool permanent)
33453350
while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
33463351
{
33473352
fputc('F', fpout);
3348-
fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
3353+
rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
3354+
(void) rc; /* we'll check for error with ferror */
33493355
}
33503356

33513357
/*

‎src/backend/utils/error/elog.c

Lines changed: 32 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1747,10 +1747,12 @@ write_eventlog(int level, const char *line, int len)
17471747
static void
17481748
write_console(const char *line, int len)
17491749
{
1750+
int rc;
1751+
17501752
#ifdef WIN32
17511753

17521754
/*
1753-
* WriteConsoleW() will fail of stdout is redirected, so just fall through
1755+
* WriteConsoleW() will fail if stdout is redirected, so just fall through
17541756
* to writing unconverted to the logfile in this case.
17551757
*
17561758
* Since we palloc the structure required for conversion, also fall
@@ -1788,13 +1790,18 @@ write_console(const char *line, int len)
17881790
#else
17891791

17901792
/*
1791-
* Conversion on non-win32 platform is not implemented yet. It requires
1793+
* Conversion on non-win32 platforms is not implemented yet. It requires
17921794
* non-throw version of pg_do_encoding_conversion(), that converts
17931795
* unconvertable characters to '?' without errors.
17941796
*/
17951797
#endif
17961798

1797-
write(fileno(stderr), line, len);
1799+
/*
1800+
* We ignore any error from write() here. We have no useful way to report
1801+
* it ... certainly whining on stderr isn't likely to be productive.
1802+
*/
1803+
rc = write(fileno(stderr), line, len);
1804+
(void) rc;
17981805
}
17991806

18001807
/*
@@ -2457,13 +2464,30 @@ send_message_to_server_log(ErrorData *edata)
24572464

24582465
/*
24592466
* Send data to the syslogger using the chunked protocol
2467+
*
2468+
* Note: when there are multiple backends writing into the syslogger pipe,
2469+
* it's critical that each write go into the pipe indivisibly, and not
2470+
* get interleaved with data from other processes. Fortunately, the POSIX
2471+
* spec requires that writes to pipes be atomic so long as they are not
2472+
* more than PIPE_BUF bytes long. So we divide long messages into chunks
2473+
* that are no more than that length, and send one chunk per write() call.
2474+
* The collector process knows how to reassemble the chunks.
2475+
*
2476+
* Because of the atomic write requirement, there are only two possible
2477+
* results from write() here: -1 for failure, or the requested number of
2478+
* bytes. There is not really anything we can do about a failure; retry would
2479+
* probably be an infinite loop, and we can't even report the error usefully.
2480+
* (There is noplace else we could send it!) So we might as well just ignore
2481+
* the result from write(). However, on some platforms you get a compiler
2482+
* warning from ignoring write()'s result, so do a little dance with casting
2483+
* rc to void to shut up the compiler.
24602484
*/
24612485
static void
24622486
write_pipe_chunks(char *data, int len, int dest)
24632487
{
24642488
PipeProtoChunk p;
2465-
24662489
int fd = fileno(stderr);
2490+
int rc;
24672491

24682492
Assert(len > 0);
24692493

@@ -2476,7 +2500,8 @@ write_pipe_chunks(char *data, int len, int dest)
24762500
p.proto.is_last = (dest == LOG_DESTINATION_CSVLOG ? 'F' : 'f');
24772501
p.proto.len = PIPE_MAX_PAYLOAD;
24782502
memcpy(p.proto.data, data, PIPE_MAX_PAYLOAD);
2479-
write(fd, &p, PIPE_HEADER_SIZE + PIPE_MAX_PAYLOAD);
2503+
rc = write(fd, &p, PIPE_HEADER_SIZE + PIPE_MAX_PAYLOAD);
2504+
(void) rc;
24802505
data += PIPE_MAX_PAYLOAD;
24812506
len -= PIPE_MAX_PAYLOAD;
24822507
}
@@ -2485,7 +2510,8 @@ write_pipe_chunks(char *data, int len, int dest)
24852510
p.proto.is_last = (dest == LOG_DESTINATION_CSVLOG ? 'T' : 't');
24862511
p.proto.len = len;
24872512
memcpy(p.proto.data, data, len);
2488-
write(fd, &p, PIPE_HEADER_SIZE + len);
2513+
rc = write(fd, &p, PIPE_HEADER_SIZE + len);
2514+
(void) rc;
24892515
}
24902516

24912517

‎src/bin/psql/common.c

Lines changed: 9 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -228,6 +228,7 @@ static void
228228
handle_sigint(SIGNAL_ARGS)
229229
{
230230
int save_errno = errno;
231+
int rc;
231232
char errbuf[256];
232233

233234
/* if we are waiting for input, longjmp out of it */
@@ -244,11 +245,16 @@ handle_sigint(SIGNAL_ARGS)
244245
if (cancelConn != NULL)
245246
{
246247
if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
247-
write_stderr("Cancel request sent\n");
248+
{
249+
rc = write_stderr("Cancel request sent\n");
250+
(void) rc; /* ignore errors, nothing we can do here */
251+
}
248252
else
249253
{
250-
write_stderr("Could not send cancel request: ");
251-
write_stderr(errbuf);
254+
rc = write_stderr("Could not send cancel request: ");
255+
(void) rc; /* ignore errors, nothing we can do here */
256+
rc = write_stderr(errbuf);
257+
(void) rc; /* ignore errors, nothing we can do here */
252258
}
253259
}
254260

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