On Sun, 13 Oct 2019 01:37:43 +0800
"Casper Ti. Vector" <caspervector_at_gmail.com> wrote:
> However, people told me that the document is not quite accessible to
> those who know really little about systemd: one example is they do not
> even know much about how the modules are organised in systemd, so the
> claim that the systemd architecture has how cohesion and high coupling
> may seem unfounded;
Hi Casper,
About not knowing how systemd modules are organized: NOBODY knows that
except Poettering et. al. To my knowledge, there has never been
published a systemd block diagram with both the blocks and the
interaction lines between those blocks. Systemd "block diagrams" are
typically a bunch of blocks in layers, which indicates nothing about
how they're organized. So if you defined how the modules were
organized, as a block diagram, you would be the first.
Contrast this situation with sane init or supervision systems. Here's my
block diagram of daemontools:
http://www.troubleshooters.com/linux/djbdns/daemontools_intro.htm#daemontools_mental_model
If I were to modify that block diagram for runit, the "system boot" and
"inittab" would be replaced by runit-init, /etc/runit/1, and
/etc/runit/2, with the latter exec'ing (being replaced by) the runit
equivalent of svscanboot.
With my understanding of s6, if I were to modify it for s6, I'd have
the s6 PID1 do some initial stuff, then exec (be replaced by) an
executable that does exactly two things:
1) Listen for and act on appropriate signals
2) Supervise the s6 supervisor, which on my diagram is svscanboot.
So with s6, PID1 becomes a supervisor that supervises one program, the
main supervisor (did I finally get that right, Laurent?)
Look at the situation. For daemontools type stuff, a guy who is a
Troubleshooting Process Trainer, an office automation Programmer, a
tech writer and an author (in other words, NOT an expert on inits) can
draw a complete and reasonably accurate block diagram including
interaction lines, whereas with systemd the millions of dollars Red Hat
spends on the "best and brightest" to produce, maintain, and evangelize
systemd cannot produce such a diagram for systemd. This is telling.
So when the systemd fanboiz tell you that you haven't provided systemd
module interaction, tell them that information is not available, and
that's excellent evidence of cohesion, high coupling, and gratuitous
complexity.
Here's another diagram I use when speaking to those who claim systemd
is modular because it has modules:
http://troubleshooters.com/linux/systemd/lol_systemd.htm
And when speaking with somebody knowledgeable enough to say that all
that gratuitous crosstalk goes through one channel, namely dbus, tell
them that doesn't matter a bit, because the crosstalk still happens.
SteveT
Steve Litt
Author: The Key to Everyday Excellence
http://www.troubleshooters.com/key
Twitter:
http://www.twitter.com/stevelitt
Received on Sat Oct 12 2019 - 18:58:59 UTC