netdev - Re: [PATCH net-next iproute2 1/3] netlink: import netlink message parsing from kernel

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Date:   Tue, 02 May 2017 14:51:02 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     dsa@...ulusnetworks.com
Cc:     stephen@...workplumber.org, netdev@...r.kernel.org,
        jakub.kicinski@...ronome.com
Subject: Re: [PATCH net-next iproute2 1/3] netlink: import netlink message
 parsing from kernel

From: David Ahern <dsa@...ulusnetworks.com>
Date: Tue, 2 May 2017 12:39:51 -0600

> On 5/2/17 12:03 PM, Stephen Hemminger wrote:
>> Then use libmnl it is already used in several other places in iproute2.
>> Eventually, I would like to use it everywhere and get rid of old netlink parser.
>> 
> 
> Why? libmnl is not going to simplify the iproute2 code.

Agreed.

> Look at attribute validation. Importing the kernel code into iproute2,
> the API is very familiar to anyone hacking on the kernel side:
> 
> +       if (nla_parse(tb, NLMSGERR_ATTR_MAX, attr, alen, extack_policy)
> != 0) {
> +               fprintf(stderr,
> +                       "Failed to parse extended error attributes\n");
> +               return 0;
> +       }
> +
> 
> ie., you pass a policy to the parse routine and the checking is part of
> nla_parse. The implementation of nla_parse and validate_nla are quite
> easy to read.
> 
> Now take a look at what devlink has for validation - attr_cb. IMO very
> unreadable and puts the burden on the app using the libmnl API.

Also agreed.

Stephen I totally agree with David, asking him to use libmnl for this is
not reasonable nor is it even a good idea given the above.