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QubesOS provides a desktop operating system made up of multiple virtual machines, running under Xen. To protect against buggy network drivers, the physical network hardware is accessed only by a dedicated (and untrusted) "NetVM", which is connected to the rest of the system via a separate (trusted) "FirewallVM". This firewall VM runs Linux, processing network traffic with code written in C. In thi
Back in July, I used MirageOS to create my first unikernel, a simple REST service for queuing file uploads, deployable as a virtual machine. While a traditional VM would be a complete Linux system (kernel, init system, package manager, shell, etc), a Mirage unikernel is a single OCaml program which pulls in just the features (network driver, TCP stack, web server, etc) it needs as libraries. Now i
Many asynchronous programs make use of promises (also known as using light-weight threads or an asynchronous monad) to manage concurrency. I've been working on tools to collect trace data from such programs and visualise the results, to help with profiling and debugging. The diagram below shows a trace from a Mirage unikernel reading data from disk in a loop. You should be able to pan around by dr
After converting 0install to OCaml, I've been looking at using more of OCaml's features to further clean up the APIs. In this post, I describe how using OCaml functors has made 0install's dependency solver easier to understand and more flexible. ( this post also appeared on Hacker News and Reddit ) Table of Contents Introduction How dependency solvers work Optimising the result The current solver
After creating my REST queuing service as a Mirage unikernel, I reported that it could serve the data at 2.46 MB/s from my ARM CubieTruck dev board. That's fast enough for my use (it's faster than my Internet connection), but I was curious why it was slower than the Linux guest, which serves files with nc at 20 MB/s. ( this post also appeared on Hacker News and Reddit ) Table of Contents The TCP t
I wanted to make a simple REST service for queuing file uploads, deployable as a virtual machine. The traditional way to do this is to download a Linux cloud image, install the software inside it, and deploy that. Instead I decided to try a unikernel. Unikernels promise some interesting benefits. The Ubuntu 14.04 amd64-disk1.img cloud image is 243 MB unconfigured, while the unikernel ended up at j
In 2013, I spent 6 months converting 0install's 29,215 lines of Python to OCaml (learning OCaml along the way). In this post, I'll describe the approach I took and how it went. There will be graphs. If you don't want to read the whole thing, the take-away is this: The new code is a similar length (slightly shorter), runs around 10x faster, and is statically type checked. ( This post also appeared
Way back in June, in Replacing Python: second round, I wrote: The big surprise for me in these tests was how little you lose going from Python to OCaml. Of course, I was mainly focused on making sure the things I needed were still available. With the port now complete (0install 2.6 has been released, and contains no Python code), here's a summary of the main things you gain. Table of Contents Func
I've now migrated the asynchronous download logic in 0install from Python to OCaml + Lwt. This post records my experiences using Lwt, plus some comparisons with Python's coroutines. As usual, the examples will be based on the real-world case of 0install, rather than on idealised text-book examples. Table of Contents The problem Solutions Callbacks Promises OCaml Lwt Python generators Examples Foll
In the first post, I took a brief look at the programming languages ATS, C#, Go, Haskell, OCaml, Python and Rust to try to decide which would be the best language in which to write 0install (which is currently implemented in Python). Now it's time to eliminate a few candidates and look in more detail at the others. Last time, I converted 4 lines of Python code from 0install into each language. Thi
This post evaluates the programming languages ATS, C#, Go, Haskell, OCaml, Python and Rust to try to decide which would be the best language in which to write 0install (which is currently implemented in Python). Hopefully it will also be interesting to anyone curious about these languages. I'm not an expert in these languages (except Python). My test-case is to read the tutorial for each language
ROX is a fast, user friendly desktop which makes extensive use of drag-and-drop. The interface revolves around the file manager, or filer, following the traditional Unix view that `everything is a file' rather than trying to hide the filesystem beneath start menus, wizards, or druids. The aim is to make a system that is well designed and clearly presented. The ROX style favours using several small
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