Almost ten months ago, I
mentioned on this
blog
I bought an ARM laptop, which is now my main machine while away from
home a
Lenovo Yoga C630
13Q50. Yes,
yes, I am still not as much
away from home as I used to before, as
this pandemic is still somewhat of a thing, but I do move more.
My main activity in the outside world with my laptop is teaching. I
teach twice a week, and well, having a display for my slides and
for showing examples in the terminal and such is a must. However, as I
said back in August, one of the hardware support issues for this
machine is:
No HDMI support via the USB-C displayport. While I don t expect
to go to conferences or even classes in the next several months,
I hope this can be fixed before I do. It s a potential important
issue for me.
It has sadly not yet been solved While many things have improved
since kernel 5.12 (the first I used), the Device Tree does not yet
hint at where external video might sit.
So, I went to the obvious: Many people carry different kinds of video
adaptors I carry a
slightly bulky one: A RPi3
For two months already (time flies!), I had an ugly contraption where
the RPi3 connected via Ethernet and displayed a VNC client, and my
laptop had a VNC server. Oh, but did I mention My laptop works
so
much better with Wayland than with Xorg that I switched, and am now a
happy user of the
Sway compositor (a drop-in
replacement for the
i3 window manager). It is
built over
WLRoots,
which is a great and (relatively) simple project, but will thankfully
not carry some of Gnome or KDE s ideas not even those I d rather
have. So it took a bit of searching; I was very happy to find
WayVNC, a VNC server for
wlroot-sbased Wayland compositors. I launched a
second Wayland, to
be able to have my main session undisturbed and present only a window
from it.
Only that VNC is slow and laggy, and sometimes awkward. So I kept
searching for something better. And something better is, happily, what
I was finally able to do!
In the laptop, I am using
wf-recorder to grab an area
of the screen and funnel it into a
V4L2 loopback
device (which allows it to
be used as a camera, solving the main issue with grabbing parts of a
Wayland screen):
/usr/bin/wf-recorder -g '0,32 960x540' -t --muxer=v4l2 --codec=rawvideo --pixelformat=yuv420p --file=/dev/video10
(yes, my V4L2Loopback device is set to
/dev/video10). You will note
I m grabbing a 960 540 rectangle, which is the top of my screen
(1920x1080) minus the Waybar. I think I ll increase it to 960 720, as
the projector to which I connect the Raspberry has a 4 3 output.
After this is sent to
/dev/video10, I tell
ffmpeg to send it via
RTP to
the fixed address of the Raspberry:
/usr/bin/ffmpeg -i /dev/video10 -an -f rtp -sdp_file /tmp/video.sdp rtp://10.0.0.100:7000/
Yes, some uglier things happen here. You will note
/tmp/video.sdp
is created in the laptop itself; this file
describes the stream s
metadata so it can be used from the client side. I cheated and copied
it over to the Raspberry, doing an ugly hardcode along the way:
user@raspi:~ $ cat video.sdp
v=0
o=- 0 0 IN IP4 127.0.0.1
s=No Name
c=IN IP4 10.0.0.100
t=0 0
a=tool:libavformat 58.76.100
m=video 7000 RTP/AVP 96
b=AS:200
a=rtpmap:96 MP4V-ES/90000
a=fmtp:96 profile-level-id=1
People familiar with RTP will scold me: How come I m streaming to the
unicast client address? I should do it to an address in the
224.0.0.0 239.0.0.0 range. And it worked, sometimes. I switched over
to 10.0.0.100 because it works, basically always
Finally, upon bootup, I have configured
NoDM to start a session with
the
user user, and dropped the following in my user s
.xsession:
setterm -blank 0 -powersave off -powerdown 0
xset s off
xset -dpms
xset s noblank
mplayer -msglevel all=1 -fs /home/usuario/video.sdp
Anyway, as a result, my students are able to much better follow the
pace of my presentation, and I m able to do some tricks better
(particularly when it requires quick reaction times, as often happens
when dealing with concurrency and such issues).
Oh, and of course in case it s of interest to anybody, knowing that
SD cards are all but reliable in the long run, I wrote a
vmdb2 recipe to build the images.
You can
grab it
here; it
requires some local files to be present to be built some are the
ones I copied over above, and the other ones are surely of no interest
to you (such as my public ssh key or such :-] )
What am I still missing? (read: Can you help me with some ideas? )
- I d prefer having Ethernet-over-USB. I have the USB-C Ethernet
adapter, which powers the RPi and provides a physical link, but I m
sure I could do away with the fugly cable wrapped around the
machine
- Of course, if that happens, I would switch to a much sexier Zero
RPi. I have to check whether the video codec is light enough for a
plain ol Zero (armel) or I have to use the much more powerful Zero
2 I prefer sticking to the lowest possible hardware!
-
Naturally The best would be to just be able to connect my
USB-C-to- HDMI,VGA adapter, that has been sitting idly One
day, I guess
Of course, this is a blog post published to brag about my stuff, but
also to serve me as persistent memory in case I need to recreate
this
I was admitted to the first cohort of students of this course (please
note I m not committing him to run free courses ever again! He has
said he would consider doing so, specially to offer a different time
better suited for people in Asia).
I have wanted to learn some Rust for quite some time. About a year
ago, I bought a copy of The Rust Programming
Language, the canonical book
for learning the language, and started reading it But lacked
motivation and lost steam halfway through, and without having done
even a simple real project beyond the simple book exercises.
How has this been? I have enjoyed the course. I must admit I did
expect it to be more hands-on from the beginning, but Rust is such a
large language and it introduces so many new, surprising
concepts. Session two did have two somewhat simple hands-on
challenges; by saying they were somewhat simple does not mean we
didn t have to sweat to get them to compile and work correctly!
I know we will finish this Saturday, and I ll still be a complete
newbie to Rust. I know the only real way to wrap my head around a
language is to actually have a project that uses it And I have
some ideas in mind. However, I don t really feel confident to approach
an already existing project and start meddling with it, trying to
contribute.
What does Rust have that makes it so different? Bufff Variable
ownership (borrow checking) and values lifetimes are the most obvious
salient idea, but they are relatively simple, as you just cannot
forget about them. But understanding (and adopting) idiomatic
constructs such as the pervasive use of enums, understanding that
errors always have to be catered for by using 
Updates
Back in April I wrote about
Years ago, it was customary that some of us stated publicly the way we
think in time of Debian General Resolutions (GRs). And even if we
didn t, vote lists were open (except when voting for people,
i.e. when electing a DPL), so if interested we could understand what
our different peers thought.
This is the first vote, though, where a Debian vote is protected under
Turns out, I have been suffering from quite bad skin infections for a
couple of years already. Last Friday, I checked in to the hospital,
with an ugly, swollen face (I won t put you through that), and the
hospital staff decided it was in my best interests to trim my
beard. And then some more. And then shave me. I sat in the hospital
for four days, getting soaked (medical term) with antibiotics and
otherstuff, got my recipes for the next few days, and well, I
really hope that s the end of the infections. We shall see!
So, this is the result of the loving and caring work of three
different nurses. Yes, not clean-shaven (I should not trim it
further, as shaving blades are a risk of reinfection).
Anyway I guess the bits of hair you see over the place will not
take too long to become a beard again, even get somewhat
respectable. But I thought some of you would like to see the real me
PS- Thanks to all who have reached out with good wishes. All is fine!
Before anything else: Go visit the
So, LibrePlanet, the FSF s conference, is coming!
I much enjoyed attending this conference in person in March 2018. This
year I submitted a talk again, and it got accepted of course, given
the conference is still 100% online, I doubt I will be able to go 100%
conference-mode (I hope to catch a couple of other talks, but well,
we are all eager to go back to how things were before 2020!)
So, what is this Storm thing? Filip promptly informed me that
Progvis is not just a pedagogical tool Or rather, that it is part
of something bigger. Progvis is a program built using 
Then, I set up the build on my own server, hosted on my Dreamhost
account and forgot about it for many months. Last month, there was
a 
I would have loved to share this earlier with the world, but The
university s processes are quite slow (and, to be fair, I also took
quite a bit of time to push things through). But today, I m finally
happy to share the result of that work with all of you. We managed to
get 11 of the talks in the colloquium as articles. The back-cover text
reads (in Spanish):
Every couple of months, one of my users falls prey to phishing
attacks, and send their login/password data to an unknown somebody
who poses as Well, as me, their always-friendly and always-helpful
systems administrator.
What follows is, of course, me spending a week trying to get our
systems out of all of the RBLs/DNSBLs. But, no matter how fast I act,
there s always distruption and lost mails (bounced or classified as
spam) for my users.
Most of my users use the Webmail I have configured on our institute s
servers, 
This FLISOL was hosted by the always great and always interesting
