[lxc-users] Mount host filesystem under /sys/class within a container

[Francesco Longo]

Any idea on this? Just a pointer to the right direction will be great!

Thanks,
Francesco

On Thu, Mar 23, 2017 at 3:52 PM, Francesco Longo <flongo at unime.it> wrote:

> Hi all,
> sorry for the very long post. As I said in a previous email I'm trying to
> play with LXD on top of a Raspberry Pi 3. My goal is to mount the GPIO
> pseudo filesystem on a container so that I can access the GPIO pins from
> within the container.
>
> I came up with the following conclusions:
>
>  - if I create a privileged container (I would prefer not to do that
> anyway) I can see the /sys/class/gpio filesystem as root but I cannot write
> it. For example, trying a classical "echo 1 > /sys/class/gpio/export, I get
> "bash: export: Read-only file system"
>  - if I create a non-privileged container I cannot even enter folder
> /sys/class/gpio as root. I can enter /sys/class but there I see that gpio
> folder has owner nobody.nogroup and 770 permissions.
>
> I solved the issue with a FUSE filesystem running on the Raspberry that
> mirrors the /sys/class/gpio and mounting such a filesystem under a
> different path, i.e., /gpio_mnt/sys/class/gpio.
>
> This is the script I created:
>
> *lxc launch ubuntu:16.04 test1*
>
> *MYUID=`sudo ls -l /var/lib/lxd/containers/test1/rootfs/ | grep root | awk
> '{}{print $3}{}'`*
>
> *lxc exec test1 -- addgroup gpio*
> *lxc exec test1 -- usermod -a -G gpio ubuntu*
> *MYGID=$(($MYUID + `lxc exec test1 -- sed -nr "s/^gpio:x:([0-9]+):.*/\1/p"
> /etc/group`))*
>
> *sudo mkdir -p /gpio_mnt/test1*
> *sudo chmod 777 -R /gpio_mnt/*
>
> *sudo mkdir -p /gpio_mnt/test1/sys/devices/platform/soc/3f200000.gpio*
> *sudo mkdir -p /gpio_mnt/test1/sys/class/gpio*
> *sudo chown "$MYUID"."$MYGID" -R /gpio_mnt/test1/sys/*
>
> *lxc exec test1 -- mkdir -p /gpio_mnt/sys/class/gpio*
> *lxc exec test1 -- mkdir -p
> /gpio_mnt/sys/devices/platform/soc/3f200000.gpio*
>
> *lxc config device add test1 gpio disk
> source=/gpio_mnt/test1/sys/class/gpio path=/gpio_mnt/sys/class/gpio*
> *lxc config device add test1 devices disk
> source=/gpio_mnt/test1/sys/devices/platform/soc/3f200000.gpio
> path=/gpio_mnt/sys/devices/platform/soc/3f200000.gpio*
>
> *#This is the mirroring through FUSE filesystem*
> *cd /home/ubuntu/test_gpio_mirroring/*
> *sudo node node-folder-mirroring.js
> /sys/devices/platform/soc/3f200000.gpio
> /gpio_mnt/test1/sys/devices/platform/soc/3f200000.gpio -o uid=$MYUID -o
> gid=$MYGID -o allow_other &> log_devices_test1 &*
> *sudo node node-folder-mirroring.js /sys/class/gpio
> /gpio_mnt/test1/sys/class/gpio -o uid=$MYUID -o gid=$MYGID -o allow_other
> &> log_gpio_test1 &*
>
> I would like not to mount under /gpio_mnt/sys/class/gpio but under
> /sys/class/gpio so that standard Raspberry libraries will work inside the
> container without any modification but I will still be able to capture the
> syscalls with the FUSE filesystem mediating the access to GPIO pins.
>
> How can I do that? Am I missing something here?
>
> Thanks,
> Francesco
>
>
> --
> ------------------------------------------------------------
> ------------------
> Dr. Francesco Longo, PhD
> Assistant Professor
> Dipartimento  di Ingegneria
> Università degli Studi di Messina
> address: Contrada di Dio (S. Agata), 98166, Messina, Italy
> email: flongo at unime.it
> phone: +39 090 3977335 <+39%20090%20397%207335> --- fax: +39 090 3977471
> <+39%20090%20397%207471>
> ------------------------------------------------------------
> ------------------
>



-- 
-------------------------------------------------------------------------------------------------
Dr. Francesco Longo, PhD

Assistant Professor @ Department of Engineering, University of Messina
address: Contrada di Dio, S. Agata - 98166, Messina, Italy
email: flongo at unime.it
web: mdslab.unime.it/flongo
phone: +39 090 3977335 --- fax: +39 090 3977471

Software Engineer @ SmartMe.io s.r.l.
address: Via Osservatorio, 1 - 98121, Messina, Italy
email: francesco at smartme.io
web: smartme.io
VAT number: 03457040834
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