Beginner Problems With TCP & The socket Module in Python
> Your operating system will deceive you and re-assemble the string you sock.recv(n) differently from the ones you sock.send(data). But here is the deceptive part. It will work sometimes, but not always. These bugs will be difficult to chase. If you have two programs communicating over TCP via the loopback device in your operating system (the virtual network device with IP 127.0.0.1), then the data does not leave your RAM, and packets are never fragmented to fit into the maximum size of an Ethernet frame or 802.11 WLAN transmission. The data arrives immediately because it’s already there, and the other side gets to read via sock.recv(n) exactly the bytestring you sent over sock.send(data). If you connect to localhost via IPv6, the maximum packet size is 64 kB, and all the packets are already there to be reassembled into a bytestream immediately! But when you try to run the same code over the real Internet, with lag and packet loss, or when you are unlucky with the multitasking/scheduling of your OS, you will either get more data than you expected, leftover data from the last sock.send(data), or incomplete data.
Not strictly a python problem, either.
ASCII table and history
> To understand why Control+i inserts a Tab in your terminal you need to understand ASCII, and to understand ASCII you need know a bit about its history and the world it was developed in. Please bear with me (or just go the table).
> Most teleprinters communicated using the ITA2 protocol. For the most part this would just encode the alphabet, but there are a few control codes: WRU (“Who R U”) would cause the receiving teleprinter to send back its identification, BEL would ring a bell, and it had the familiar CR (Carriage Return) and LF (Line Feed).
DragonFly kcollect(8) improvements
> DragonFly has a utility called kcollect(8), for gathering about the last day’s worth of kernel statistics. It recently gained some extra flags and details, and should work well if you want to collect stats in a low-impact way.
A one liner to rename files.
> ls | grep ‘aaa’ | sed ‘p;s/aaa/bbb/’ | xargs -n2 | xargs -L1 bash -c ‘mv $0 $1’
A literary appreciation of the Olson/Zoneinfo/tz database
> What I didn’t appreciate, until I finally unzipped and untarred a copy of ftp://elsie.nci.nih.gov/pub/tzdata2009o.tar.gz, is the historical scholarship scribbled in the margins of this remarkable database, or document, or hybrid of the two.
DragonFly BSD 5.6
> DragonFly version 5.6 brings an improved virtual memory system, updates to radeon and ttm, and performance improvements for HAMMER2.
Improvements in forking, threading, and signal code
> I am improving signaling code in the NetBSD kernel, covering corner cases with regression tests, and improving the documentation. I’ve been working at the level of sytems calls (syscalls): forking, threading, handling these with GDB, and tracing syscalls. Some work happens behind the scenes as I support the work of Michal Gorny on LLDB/ptrace features.
dragonfly - Add initial FUSE support
> The basic code design comes from FreeBSD, but the code is written from scratch. It was just easier to write from scratch than trying to port sys/fs/fuse/* in FreeBSD for various reasons. Note that this is to implement FUSE API/ABI, but not to be compatible with FreeBSD implementation which contains FreeBSD specific sysctls, etc.
ufs - Expand time_t support to 48 bits
> Fix time overflow issues in the original 32-bit UFS code in two ways. First, treat the original 32-bit seconds fields as unsigned.Second, utilize the spare fields to expand these fields to 48 bits each. Retain the nanosecond-grain accuracy of the nsec fields.
Schedule 35th Chaos Communication Congress
The Super Capsicumizer 9000
> capsicumizer is a sandbox launcher that imposes Capsicum capability mode onto an unsuspecting program, allowing “sysadmin style” or “oblivious” sandboxing (i.e. no source code modifications, all restrictions added externally).
Choosing error codes based on a really nice #define doesn’t necessarily lead to a readable message to the user
> What happened is that the program was using some internal helper object. If somebody tries to use the object before it has been properly configured, the developer needed to return an error code to indicate this. The developer went cruising through winerror.h looking for a suitable error code, and hey look, here’s one: ERROR_NOT_READY. Awesome, let’s return that error code.
> But what the developer didn’t check is how that error message looks to the user. The function that displays the error code to the user will use the FormatMessage function to perform the error-code-to-message conversion. And that produces “The device is not ready“, which is nonsense.
Applies to quite a few posix errno values as well.
DragonFly BSD 5.4
> DragonFly version 5.4 brings a new system compiler in GCC 8, improved NUMA support, a large of number network and virtual machine driver updates, and updates to video support.
Demonstration of various hardware effects
> This repository demonstrates various hardware effects that can degrade application performance in surprising ways and that may be very hard to explain without knowledge of the low-level CPU and OS architecture. For each effect I try to create a proof of concept program that is as small as possible so that it can be understood easily.
> Those effects obviously depend heavily on your CPU microarchitecture and model, so the demonstration programs may not showcase the slowdown on your CPU, but I try to make them as general as I can. That said, the examples are targeting x86-x64 processors (Intel and AMD) and may not make sense on other CPU architectures. I try to make them compatible with Windows, but they are mainly tested on Linux.
> I spent a couple of years evangelizing about Capsicum. I wrote many articles about it. So, it is very natural that I would also like to update you on this blog about the progress of the Capsicum project in FreeBSD, because this is what I’m doing in my free time. That said I feel that this blog wouldn’t be completed without some introduction to what Capsicum is. This post should fill this gap. Over the next weeks and months we will extend this topic and discuss different parts of Capsicum.
Exploring the Future Beyond Cyberpunk’s Neon and Noir
> Which microgenres are bubbling up, and which trends and themes best describe how creators are imagining the future? Here are nine suggestions.
Dive into syscall handling on freeBSD AMD64
Why Aren’t More Users More Happy With Our VMs?
> In the process of using the Kalibera and Jones methodology, we noticed quite a lot of variation in the warmup time of different VMs and cases where VMs didn’t seem to warmup at all. This was surprising because pretty much every paper we’d read until that point had assumed – and, in many cases, explicitly stated – that warmup was a quick, consistent, thing. On that basis, it seemed interesting to see how the warmup time of different VMs compared. In May 2015, I asked Edd if he’d knock together a quick experiment in this vein, estimating that it would take a couple of weeks. After a couple of weeks we duly had data to look at but, to put it mildly, it wasn’t what we had expected: it showed all sorts of odd effects. My first reaction was that if we showed this data to anyone else without checking it thoroughly, we’d be in danger of becoming a laughing stock. It was tempting to bury my head in the sand again, but this time it seemed like it would be worth digging deeper to see where we’d gone wrong.
Be careful what you measure. You may not like the result...
Part 2: https://tratt.net/laurie/blog/entries/why_arent_more_users_more_happy_with_our_vms_part_2.html
Hidden gems of xterm
A setting for every config and a config for every setting.
> This application visualizes the relationships between the convex, regular-faced polyhedra. The 120 solids presented here can be transformed into each other by a network of operations.