MDEV-15584 Linux use O_TMPFILE

O_TMPFILE creates a tempfile not attached to a filename.

This is what we want for MY_TEMPORARY.

We preserve a state O_TMPFILE_works, because kernel version or
filesystem could cause failure.

Closes #662

include/my_sys.h

@@ -328,7 +328,7 @@ typedef struct st_record_cache	/* Used when caching records */
 enum file_type
 {
   UNOPEN = 0, FILE_BY_OPEN, FILE_BY_CREATE, STREAM_BY_FOPEN, STREAM_BY_FDOPEN,
-  FILE_BY_MKSTEMP, FILE_BY_DUP
+  FILE_BY_O_TMPFILE, FILE_BY_MKSTEMP, FILE_BY_DUP
 };
 
 struct st_my_file_info

mysys/mf_tempfile.c

@@ -110,6 +110,33 @@ File create_temp_file(char *to, const char *dir, const char *prefix,
     }
   }
 #elif defined(HAVE_MKSTEMP)
+#ifdef O_TMPFILE
+  {
+    static int O_TMPFILE_works= 1;
+
+    if ((MyFlags & MY_TEMPORARY) && O_TMPFILE_works)
+    {
+      /* explictly don't use O_EXCL here has it has a different
+         meaning with O_TMPFILE
+      */
+      if ((file= open(dir, mode | O_TMPFILE | O_CLOEXEC,
+                      S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP)) >= 0)
+      {
+        my_snprintf(to, FN_REFLEN, "%s/#sql/fd=%d", dir, file);
+        file=my_register_filename(file, to, FILE_BY_O_TMPFILE,
+                                  EE_CANTCREATEFILE, MyFlags);
+      }
+      else if (errno == EOPNOTSUPP || errno == EINVAL)
+      {
+        my_printf_error(EE_CANTCREATEFILE, "O_TMPFILE is not supported on %s "
+                        "(disabling future attempts)",
+                        MYF(ME_NOTE | ME_ERROR_LOG_ONLY), dir);
+        O_TMPFILE_works= 0;
+      }
+    }
+  }
+  if (file == -1)
+#endif /* O_TMPFILE */
   {
     char prefix_buff[30];
     uint pfx_len;