Ceph » rbd

I was recently working on a patch for krbd, and was dismayed to discover
that the rbd tool wouldn't pass through a new kernel option that I had
added. Looking at the code, we have a lot off places where we just
"hand-off" options to the kernel, and then we return -EINVAL on anything
that the userland program doesn't know about:

    } else if (!strcmp(this_char, "udev") || !strcmp(this_char, "noudev")) {
        put_map_option("udev", this_char, map_options);
    } else {
        std::cerr << "rbd: unknown map option '" << this_char << "'" << std::endl;                    
        return -EINVAL;
    }

Kernel mount helper programs usually just pass through options that they
don't recognize, so we (usually) don't need to deploy both a new kernel
and userspace program to use a new mount option.

Make rbd work the same way. Instead of erroring out when it doesn't recognize an option, just have it pass it through to the kernel as-is.