How to add a namespaced instance value

[jorgensigvardsson]

Hi,

I'm currently populating state in a state callback, and I keep getting LY_EVALID errors when I try to populate a path with values from another module. I'm actually trying to populate /ietf-interfaces:interfaces/interface[name='foo']/type with a value from iana-if-type.

How would I go about to do this? I can't find any example of this neither on github nor in the documentation for libyang. Thanks!

[michalvasko]

I understand it may not be simple to find the first time but all the information should be there and referencing further relevant docs. I assume you are using lyd_new_path() and the docs for value mention JSON format. That is defined in an RFC, where you can read about how an identityref value should be represented. Feel free to suggest what to improve in the docs for other users to find it next time.

[jorgensigvardsson]

Yeah, I saw that reference, but it doesn't really work, or I'm missing something.

So ietf-interfaces has an identity interface-type. iana-if-type has a bunch of identities based on interface-type. If I want to use ethernetCsmacd for instance, what prefix should I use? ietf-interfaces does not import iana-if-type, so I can't use a prefix in that module. If I use the module name (iana-if-type) as a prefix, I still get the validation error.

Values I've tried:

• ethernetCsmacd
• iana-if-type:ethernetCsmacd

Could it be that the module is not loaded?

[jorgensigvardsson]

The module is loaded by sysrepo (output from sysrepoctl -l)

iana-if-type                  | 2021-06-21 | I     | root:root | 600         |            | 

[michalvasko]

iana-if-type:ethernetCsmacd is the correct one, examine the error you get to learn what is wrong (ly_err_msg() on the context).

[jorgensigvardsson]

This is awkward, I fed it the wrong value. 😫 I had a mapping function that maps from Linux interface type values into strings via a string table. The problem is that I returned a string from another table (oper-status). The ly_errmsg() did wonders. Thanks!

I really need to get more sleep these days.

[michalvasko]

Sorry for misspelling the function name...

[jktjkt]

You need to explicitly install/implement the model which provides the YANG identities.

And just FYI, there are already two projects which deal with the ietf-interfaces YANG model:

• velia which generates config for systemd-networkd and which reads runtime data via libnl (see this example code for how it populates the type leaf)
• sysrepo-plugin-interfaces which configures interfaces directly via libnl IIRC

Perhaps using one of these projects might save you some development time? I know that we're happy to accept patches for velia, and I expect that it will be the same for sysrepo-plugin-interfaces.

[jorgensigvardsson]

I've looked at both these projects, but the way they're implemented doesn't rhyme well with the goal architecture I'm working against. We have a ton of software written for an older generation of the platform, that we want to continue working on a new version of the platform w/ as few changes as possible.

I'm not saying it can't be done, but we'd probably have to fork such projects, because our changes would most likely not be accepted upstreams.

It's a shame, because I prefer OSS collaboration. Win/win for everyone.