Setting mount options for USB drive filesystem

[EmeraldDeer]

I would like to set mount options for USB drive filesystems.
I tried setting "usb_ext_opt" to "data=journal,discard" according to the snippet of rc/usb.c below but it did not take effect and the nvram variable is now empty.
Does anyone know the sprintf syntax below? Perhaps I have it wrong.

        if (strcmp(type, "swap") == 0 || strcmp(type, "mbr") == 0) {
            /* not a mountable partition */
            flags = 0;
        }
        else if (!strcmp(type, "unknown")) {
            /* Usually should be EFI, and not a mountable partition */
            flags = 0;
        }
        else if(!strncmp(type, "ext", 3)){
            sprintf(options, "user_xattr");

            if (nvram_invmatch("usb_ext_opt", ""))
                sprintf(options + strlen(options), "%s%s", options[0] ? "," : "", nvram_safe_get("usb_ext_opt"));
        }
        else if (strcmp(type, "vfat") == 0) {
            sprintf(options, "umask=0000");