Add data and root partition full warning / notification.

[mpvader]

Relates mostly to people using large image. The full data partition is most valuable, since that affects our main use case (node-red); and full root partition is for all the tinkerers and people with mods.

(note that I'm only 99% sure that a full root partition is not normal - Jeroen will know for sure).

some data from the system that got me here:

root@einstein:~# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/root               972392    927788         0 100% /
devtmpfs                465376         4    465372   0% /dev
tmpfs                   515040      1016    514024   0% /run
tmpfs                   515040       576    514464   0% /var/volatile
/dev/mmcblk1p5         1134336   1059272         0 100% /data
/dev/mmcblk0p1        15538856      1280  15537576   0% /run/media/mmcblk0p1
tmpfs                   515040      1016    514024   0% /service
overlay                 515040       576    514464   0% /var/lib
root@einstein:~# cd /data
root@einstein:/data# ls
123SmartBMS-Venus     VeCanSetup            etc                   log                   reinstallScriptsList  var
GuiMods               conf                  home                  lost+found            setupOptions          venus
SetupHelper           db                    keys                  rcS.local             themes                vrmfilescache
root@einstein:/data# du -d 3 /data | sort -nr
1055788	/data
1039424	/data/conf
1039320	/data/conf/signalk
71048	/data/conf/signalk/node_modules
64224	/data/conf/signalk/.npm
7188	/data/conf/signalk/.cache
7032	/data/GuiMods
6348	/data/log
6208	/data/GuiMods/FileSets
1700	/data/GuiMods/FileSets/v3.20~36

[mpvader]

hey @mansr , as discussed - any preference on what system calls to use to check for free disk space?

Do we need to try write a file? Or can some simple standard call checking for free diskspace be used?

[kwindrem]

I use

availableSpace=$(df -m / | tail -1 | awk '{print $4}')
to check fullness in SetupHelper. -m returns available space in megabytes.

This is called from a shell script but could also be done via a procedure call in python.

[mansr]

I would suggest checking both free space (blocks) and free inodes (files). In a shell script, stat -f will print these values. From C or C++, use the statvfs system call, also available in Python as os.statvfs. What thresholds to use for a warning will need some consideration. If we want to get fancy, we could even warn if the rate of change over an hour (or maybe day) is too high. That might alert the user to take action before it becomes urgent.