Save open's errno when opening temp rdb fails to prevent it from bein…

…g modified

Apparently on Mac, sleep will modify errno to ETIMEDOUT, and then it
prints the misleading message: Operation timed out.

Signed-off-by: Binbin <[email protected]>

src/replication.c

@@ -3684,13 +3684,18 @@ void syncWithPrimary(connection *conn) {
 
     /* Prepare a suitable temp file for bulk transfer */
     if (!useDisklessLoad()) {
+        /* We save the errno of open to prevent some systems from modifying it after
+         * the sleep call. For example, sleep in Mac will change errno to ETIMEDOUT. */
+        int saved_errno;
         while (maxtries--) {
             snprintf(tmpfile, 256, "temp-%d.%ld.rdb", (int)server.unixtime, (long int)getpid());
             dfd = open(tmpfile, O_CREAT | O_WRONLY | O_EXCL, 0644);
             if (dfd != -1) break;
+            saved_errno = errno;
             sleep(1);
         }
         if (dfd == -1) {
+            errno = saved_errno;
             serverLog(LL_WARNING, "Opening the temp file needed for PRIMARY <-> REPLICA synchronization: %s",
                       strerror(errno));
             goto error;