index concept papers



Values Palette
.

Here, we consider design qualities that could influence the design of a
platform.

 [!] This is not a set of design principles for dinghy.

Rather: in order to think, we look at possibilities.


Cheap process forking

    Unix has this.

    Unix developers can compose systems by creating and leaning on many
    processes, and on short-lived processes.

    Cheap process forking encourages the unix piping mechanism. Upside: allows
    for rapid composition of complex pipelines from simple tools. Downside:
    requires lots of copying of memory from one process space to the next.

    The early apache webserver httpd handled CGI through such a strategy: the
    server spawned a new child process for each request.

    Upside: Offloads lots of nasty concurrency problems onto the operating
    system, which has already had to solve those problems.
    
    Downside: does not scale as well as later single-process efforts like
    apache 2 (uses threads) and nginx (focus on async techniques).

    Summary: cheap process forking is good for prototyping, bad for scale.


Network-centric filesystem

    Most commonly seen in institutions with lots of unix systems arranged
    around a large NFS filesystem held on high-cost equipment.

    Has practical value. A dedicated team can ensure data is backed up. You
    can log in from any system. You can easily share data between operators.

    Network-centric filesystem is an anti-pattern in some some settings. If
    you are processing lots of data, network-centric filesystems encourage
    users to be in a mindset of drawing data to work. At scale, it is better
    to instead send work to data.


Everything is a File

    This is contested territory. We will handle it through different
    perspectives, below.

    Everything is a File (Stream of Bytes)

        This is the unix way.

        There is a central hierarchical filesystem.

        Things that are not data-stored-on-disk can be attached to the
        hierarchy as though they were, and you can interact with them using
        the same tools as you would use to interact with data-stored-on-disk.
        (Kind of. Some of the time.)

        There is some elegance. You can use select(2) to detect non-blocking
        behaviour across both files and sockets and stdin. Kind of. This is
        not at all possible in Windows.

        There is some inelegance. Lots of edge-cases. Calling select(2) on
        files does not behave the same as calling it on network sockets. There
        are things you can't write to.

        Linus wrote,

            The whole point with "everything is a file" is not that you have
            some random filename (indeed, sockets and pipes show that "file"
            and "filename" have nothing to do with each other), but the fact
            that you can use common tools to operate on different things.

        And later,

            The UNIX philosophy is often quoted as "everything is a file", but
            that really means "everything is a stream of bytes".

            In Windows, you have 15 different versions of "read()" with
            sockets and files and pipes all having strange special cases and
            special system calls. That's not the UNIX way. It should be just a
            "read()", and then people can use general libraries and treat all
            sources the same.

        https://yarchive.net/comp/linux/everything_is_file.html

    Everything is a File (Namespace emphasis)

        This is the plan-9 way.

        Plan-9 achieves minimalism through rigid structuring of the system
        into namespaces that look like filesystems.

        Linus uses the term {Everything is a namespace} to contrast the Plan-9
        ethos from the {Everything is a stream of bytes} principle as he
        interprets it.

        In Plan-9, there is a standard interface (namespace) that presents as
        though it is a filesystem. Applications present as filesystems.
        Network connections present like filesystems. The system interface
        presents like a filesystem.

        Consequently, the Plan 9 system-call interface is very small.

        The system is discoverable. You can browse around /proc and look for
        things.

        It can take effort to build all applications so as to honour this
        interface. How do you implement a web browser such that it exposes
        itself as a namespace? Perhaps this speaks less of plan-9 failure, and
        instead of what a terrible settlement the web is.


    Everything is an icon

        The BeOS/Haiku way

        A variety of concepts are exposed to a browsable GUI as icons.

        Concept of a hierarchical filesystem.

        Icons represent metadata and an optional stream of data (file).
        
        Sophisticated use of metadata tags leads to an innovative type of
        naked application. In one example, users interact with email without
        the use of an email client. A daemon draws mail down into icons as it
        arrives. Users use the standard OS GUI to view their set of email.
        There are small, distinct programs for viewing and writing email.

        This hints at a design tradition to rival vs monolithic applications
        such as Outlook and Photoshop.

        Imagine an art program where each layer was a file in a directory.
        
        more

        With that said, I am wary of this as a design principle.

        IPC-via-filesystem suffers from tragedy-of-the-common interface bleed.
        Imagine reading a file and expecting to see X or Y. But the writer
        wrote Z. Who is at fault?


Everything is an interface

    Imagine an operating system where there was no filesystem. Rather, you had
    to interact with interfaces. You could use existing tools to construct new
    types and interfaces, and then interact with those.

    Consider: how to interact with the network, which produces data that is
    outside your sphere of control.


The Memory Map is the Computer

    What is the essence of the computer?

    Here we consider that it could be the memory map.

    Computer architectures often presents several types of memory in a single
    memory map. By accessing addresses A to B, you can read from ROM.
    Addresses B to C will hook into standard RAM. Addresses C to D will hook
    into video ram.

    Potentially, you could build an instruction architecture strictly oriented
    around reads and writes to memory. You could even implement mathematics
    operations as a consequence of writing to fake addresses.

    What behaviour would we expect when the program attempts to divide by
    zero?


The CPU is the Computer

    What is the essence of the computer?
    
    Someone might point to the Central Processing Unit. You can tell by its
    name that it is the heart of the computer.

    The CPU reads from memory and writes to memory, and thereby drives
    activity.

    Computers are inherently synchronous.


The Bus is the Computer

    What is the essence of the computer?

    It is the bus.
    
    The term CPU is a misnomer. Processing cores are simply peers on a bus.

    Operations come and go: user input, network interaction, interrupts.

    Computers are inherently asynchronous.


The Backbone is the Computer

    This strictly follows the logic of "The Bus is the Computer" to a further
    conclusion.

    Picture a system which is a set of computers arranged around a private,
    contained network. They are running different nodes of a single deployment
    of a software system.

    Operations come and go. Computers are simply peers on a bus.

    Computers are inherently asynchronous.


Multi-threading

    Mainstream operating systems are generally synchronous. Mainstream
    applications are generally asynchronous. Multithreading is a means for
    bridging those two worlds.


Pure async

    Speculation: what about an OS where all system interactions were based on
    callback?

    Tannenbaum comments


GUI-driven development

    Applications where the developer starts with a GUI, and then works out the
    data structures later.

    Examples,
    - Programs written in Visual Basic
    - Programs written in Interface Builder/WO
    - Stuff build for MacOS classic

    Problem: data structures tend to be a mess. Concurrency tends to be a
    mess.


Outliner-driven development

    Userland Frontier presents an outliner as the entrypoint into the system.

    http://frontier.userland.com/

    (Need to do work here. Waiting on a house move to unpack my computers)


User is a Guest

    Positive: System is Lord Protector

        Computers are necessarily complicated.

        System software has a duty to silently run things in an orderly
        manner, The user should only be exposed to things they are likely to
        care about.

    Negative: System is Jailor

        Computers are not necessarily complicated.

        Systems software should not make the owner feel like a guest in their
        own home.


FPGAs

    Positive: Liquid hardware is Awesome

        Microchips are obsolete.

        We can build what we want in FPGAs.
        
        We can create hardware without needing to get our hands dirty again.

        We can easily create extra layers.


    Negative: Liquid hardware is Terrifying

        Intel has put lots of hidden layers into our main computing platform. The
        security is dodgy.

        Unless we are careful, all those problems are going to get a lot worse
        with FPGAs. How could you know if your FPGA had been backdoored?

        We should be wary of every layer.