netdev - Re: How to display IPv4 array?

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Message-ID: <ZfBMbZRbgwFOFPmk@Laptop-X1>
Date: Tue, 12 Mar 2024 20:37:01 +0800
From: Hangbin Liu <liuhangbin@...il.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Jakub Kicinski <kuba@...nel.org>,
	Donald Hunter <donald.hunter@...il.com>, netdev@...r.kernel.org
Subject: Re: How to display IPv4 array?

Hi Jiri,
On Tue, Mar 12, 2024 at 01:12:30PM +0100, Jiri Pirko wrote:
> Tue, Mar 12, 2024 at 11:08:33AM CET, liuhangbin@...il.com wrote:
> >Hi Jakub,
> >
> >I plan to add bond support for Documentation/netlink/specs/rt_link.yaml. While
> >dealing with the attrs. I got a problem about how to show the bonding arp/ns
> >targets. Because the arp/ns targets are filled as an array[1]. I tried
> >something like:
> >
> >  -
> >    name: linkinfo-bond-attrs
> >    name-prefix: ifla-bond-
> >    attributes:
> >      -
> >        name: arp-ip-target
> >        type: nest
> >        nested-attributes: ipv4-addr
> >  -
> >    name: ipv4-addr
> >    attributes:
> >      -
> >        name: addr
> >        type: binary
> >        display-hint: ipv4
> >
> >But this failed with error: Exception: Space 'ipv4-addr' has no attribute with value '0'
> >Do you have any suggestion?
> >
> >[1] https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/tree/drivers/net/bonding/bond_netlink.c#n670
> 
> Yeah, that's odd use of attr type, here it is an array index. I'm pretty
> sure I saw this in the past on different netlink places.
> I believe that is not supported with the existing ynl code.
> 
> Perhaps something like the following might work:
>       -
>         name: arp-ip-target
>         type: binary
>         display-hint: ipv4
> 	nested-array: true
> 
> "nested-array" would tell the parser to expect a nest that has attr
> type of value of array index, "type" is the same for all array members.
> The output will be the same as in case of "multi-attr", array index
> ignored (I don't see what it would be good for to the user).

Yes, this looks a do-able way. Although we already have a similar type
'array-nest'...

I also figured out a workaround. e.g.

  -
    name: linkinfo-bond-attrs
    name-prefix: ifla-bond-
    attributes:
      -
        name: arp-ip-target
        type: nest
        nested-attributes: ipv4-addr

  -
    name: ipv4-addr
    attributes:
      -
        name: addr0
        value: 0
        type: u32
        byte-order: big-endian
        display-hint: ipv4
      -
        name: addr1
        value: 1
        type: u32
        byte-order: big-endian
        display-hint: ipv4

With this we can show the target like:

     'arp-ip-target': {'addr0': '192.168.1.1',
                       'addr1': '192.168.1.2'},

But we need to add all BOND_MAX_ARP_TARGETS attrs. Which doesn't like a good
way. So maybe as you suggested, add a new type "nested-array".

Thanks
Hangbin