How can iio_info find "context" of two chained boards each with their own libiio/iiod?

This is a feature of iiod already. See this commit: https://github.com/analogdevicesinc/libiio/commit/94c43cea5f9b2a2ddbc3d1ee5d60746fef4274ee

-Travis

Thank you Travis,

It's the "run iiod and allow the USB context to be "bridged" to Ethernet to other remote hosts" that I'm not quite getting right.

With A->C->B chained devices, the following shows iio_info running on A and getting a response from iiod running on C ... but not from B:

dev@dev-VirtualBox:~/SVNviews_local/libiio/build/tests$ iio_info --uri ip:192.168.10.100
Library version: 0.24 (git tag: a08ad5f)
Compiled with backends: local xml ip usb
IIO context created with network backend.
Backend version: 0.24 (git tag: a08ad5f)
Backend description string: 192.168.10.100 Linux imx6ul-var-dart 4.14.78-mx6ul+ge692c30 #1 SMP PREEMPT Fri Aug 21 09:21:40 UTC 2020 armv7l
IIO context has 3 attributes:
       local,kernel: 4.14.78-mx6ul+ge692c30
       uri: ip:192.168.10.100
       ip,ip-addr: 192.168.10.100

Also the following shows iio_info running on C and getting a response from its own local context and from iiod running on B:

root@imx6ul-var-dart:~/libiio-tests# ./iio_info --scan
Library version: 0.24 (git tag: a08ad5f)
Compiled with backends: local xml ip usb
Available contexts:
	0: 192.168.1.2 ) [ip:imx6ul-var-dart.local]
	1: 192.168.10.100 ) [ip:imx6ul-var-dart.local]
	2: 192.168.2.10 ) [ip:imx6ul-var-dart.local]
	3: 192.168.2.1 (Analog Devices PlutoSDR Rev.B (Z7010-AD9363A)), serial=104473ae7393000101003600085f2dbec1 [ip:pluto.local]
	4: (2198000.adc on Variscite DART-6UL with i.MX6ULL, eMMC & WiFi support on VAR-6ULCustomBoard) [local:]
	5: 0456:b673 (Analog Devices Inc. PlutoSDR (ADALM-PLUTO)), serial=104473ae7393000101003600085f2dbec1 [usb:2.2.5]

So I've noticed that B (Pluto) is on a different subnet from A (PC) ... so perhaps my problem is that I need to learn how to bridge two subnets. Doh!

Kind regards

DrFlute

What arguments are you using to run iiod?

-Travis

I'm starting iiod on C manually but without any arguments. The iiod on B (Pluto) is run automatically ... and it would probably be a good idea if I looked at the startup script that runs it ... and report back soon.

As you can see from that commit I linked you need to tell the bridging iiod which context it needs to relay with the uri flag.

-Travis

Well the Pluto says:

# grep -rnw /etc -e iiod
grep: /etc/resolv.conf: No such file or directory
/etc/init.d/S23udc:114: start-stop-daemon -S -b -q -m -p /var/run/iiod.pid -x  /usr/sbin/iiod  -- $IIOD_OPTS

...and

# grep -rnw /etc -e IIOD_OPTS
grep: /etc/resolv.conf: No such file or directory
/etc/init.d/S23udc:7:IIOD_OPTS="-D -n $ENDPOINTS -F /dev/iio_ffs"

... and 

# grep -rnw /etc -e ENDPOINTS
grep: /etc/resolv.conf: No such file or directory
/etc/init.d/S23udc:7:IIOD_OPTS="-D -n $ENDPOINTS -F /dev/iio_ffs"
/etc/device_config:4:ENDPOINTS=3

So I think this all amounts to:
/usr/sbin/iiod -- -D -n 3 -F /dev/iio_ffs

... and you've just replied ahead of m e...

OK ... so I need to start iiod on C with an argument that says it should relay the context of B (Pluto) by using the uri flag. I'll try that right away.

OK ... so I'm getting further ... but it's not great.

This is starting iiod on C using the ip address of B (Pluto) ... and the "ERROR: READ LINE: -32" start when I run iio_info on A

root@imx6ul-var-dart:~/libiio-tests# ./iiod --uri ip:192.168.2.1
Starting IIO Daemon version 0.24.a08ad5f
IPv6 support enabled
Attempting to start Avahi
ERROR: host imx6ul-var-dart
Avahi: Registered 'iiod on imx6ul-var-dart:30431' to ZeroConf server avahi 0.7
Avahi: Started.
Avahi: Service 'iiod on imx6ul-var-dart:30431' successfully established.
New client connected from 0.0.0.0
ERROR: READ LINE: -32
ERROR: READ LINE: -32
ERROR: READ LINE: -32
ERROR: READ LINE: -32
ERROR: READ LINE: -32

... and this is the response from A, at least trying to report attributes of Pluto

dev@dev-VirtualBox:~/SVNviews_local/libiio/build/tests$ iio_info --uri ip:192.168.10.100
Library version: 0.24 (git tag: a08ad5f)
Compiled with backends: local xml ip usb
IIO context created with network backend.
Backend version: 0.23 (git tag: v0.23)
Backend description string: 192.168.10.100 Linux (none) 5.4.0-00535-g9c04de11ae53 #1 SMP PREEMPT Fri Aug 20 13:01:03 CEST 2021 armv7l
IIO context has 9 attributes:
	hw_model: Analog Devices PlutoSDR Rev.B (Z7010-AD9363A)
	hw_model_variant: 1
	hw_serial: 104473ae7393000101003600085f2dbec1
	fw_version: v0.34
	ad9361-phy,xo_correction: 39999923
	ad9361-phy,model: ad9363a
	local,kernel: 5.4.0-00535-g9c04de11ae53
	uri: ip:192.168.10.100
	ip,ip-addr: 192.168.10.100
IIO context has 5 devices:
...
				attr  4: hardwaregain ERROR: Broken pipe (32)
...

That's enough for today.

Thank you very much for your help Travis

Kind regards
DrFlute

So ... the solution to my problem of chaining boards A -> C -> B where  

A=PC
C=DART-6UL
B=ADALM-PLUTO

and 

A -> C is ethernet
C -> B is usb

is ...

1) run iiod on C with the ip address of B and with the same command line arguments as the iiod run on B: ./iiod  -D -n 3 --uri ip:192.168.2.1  

2) run iio_info on A with the ip address of C: iio_info --uri ip:192.168.10.100

Now I can run IIO Oscilloscope on A and have it present a spectrum of samples from B relayed via C.

I hope this helps someone with the same problem ... and thanks to Travis for pointing me in the right direction.

Kind  regards
DrFlute