Question about /proc/net/netlink mystery

Question about /proc/net/netlink mystery

[Rami Rosen]

Hi,
I tried to figure this out, but something is mysterious here to me.

 cat /proc/net/netlink
shows:
sk       Eth Pid    Groups   Rmem     Wmem     Dump     Locks

Why is the Eth here in the second column title?
It does not seem that this column has anything to do with network
interfaces.

A short look to the code, in netlink_seq_show() , net/netlink/af_netlink.c,
will show that the values in this column are s->sk_protocol.

So it seems that the title should be here different; it should represent
the protocol (since s->sk_protocol is assigned
the number of the protocol of the netlink socket ;
for example, NETLINK_ROUTE is 0, NETLINK_AUDIT is 9, and so on ; (see
include/linux/netfilter.h)

So shouldn't it be something like "Proto"?

Regards,
Rami Rosen

Re: Question about /proc/net/netlink mystery

[Neil Horman]

On Wed, May 20, 2009 at 10:22:46PM +0300, Rami Rosen wrote:
> Hi,
> I tried to figure this out, but something is mysterious here to me.
> 
>  cat /proc/net/netlink
> shows:
> sk       Eth Pid    Groups   Rmem     Wmem     Dump     Locks
> 
> Why is the Eth here in the second column title?
> It does not seem that this column has anything to do with network
> interfaces.
> 
> A short look to the code, in netlink_seq_show() , net/netlink/af_netlink.c,
> will show that the values in this column are s->sk_protocol.
> 
> So it seems that the title should be here different; it should represent
> the protocol (since s->sk_protocol is assigned
> the number of the protocol of the netlink socket ;
> for example, NETLINK_ROUTE is 0, NETLINK_AUDIT is 9, and so on ; (see
> include/linux/netfilter.h)
> 
> So shouldn't it be something like "Proto"?
> 
Someone might have been mistakenly thinking [Eth]ertype for that field, but
regardless, it seems wrong.  Honestly, The colum should likely be proto, but who
knows what apps parsing you break if you make that change now.

Neil

> Regards,
> Rami Rosen
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Re: Question about /proc/net/netlink mystery

[Ben Hutchings]

On Wed, 2009-05-20 at 22:22 +0300, Rami Rosen wrote:
> Hi,
> I tried to figure this out, but something is mysterious here to me.
> 
>  cat /proc/net/netlink
> shows:
> sk       Eth Pid    Groups   Rmem     Wmem     Dump     Locks
> 
> Why is the Eth here in the second column title?
> It does not seem that this column has anything to do with network
> interfaces.
> 
> A short look to the code, in netlink_seq_show() , net/netlink/af_netlink.c,
> will show that the values in this column are s->sk_protocol.

I would guess that "Eth" is meant to be short for "Ethertype", a
layer-3 protocol number, although sock::sk_protocol actually holds a
layer-4 protocol number.

> So it seems that the title should be here different; it should represent
> the protocol (since s->sk_protocol is assigned
> the number of the protocol of the netlink socket ;
> for example, NETLINK_ROUTE is 0, NETLINK_AUDIT is 9, and so on ; (see
> include/linux/netfilter.h)
> 
> So shouldn't it be something like "Proto"?

Yes, but changing column names in /proc risks breaking the programs that
read them.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

Re: Question about /proc/net/netlink mystery

[David Miller]

From: Ben Hutchings <bhutchings@solarflare.com>
Date: Wed, 20 May 2009 20:51:03 +0100

> On Wed, 2009-05-20 at 22:22 +0300, Rami Rosen wrote:
>> So it seems that the title should be here different; it should represent
>> the protocol (since s->sk_protocol is assigned
>> the number of the protocol of the netlink socket ;
>> for example, NETLINK_ROUTE is 0, NETLINK_AUDIT is 9, and so on ; (see
>> include/linux/netfilter.h)
>> 
>> So shouldn't it be something like "Proto"?
> 
> Yes, but changing column names in /proc risks breaking the programs that
> read them.

Indeed, it's odd, but like others I don't think we can change it
at this point.