Re: kern/110720: [net] [patch] support for interface descriptions

On Sat, Mar 24, 2007 at 06:37:59PM +0100, Hartmut Brandt wrote:
On Sat, 24 Mar 2007, Eugene Grosbein wrote:

EG>On Sat, Mar 24, 2007 at 11:30:44AM +0100, Andre Oppermann wrote:
EG>
EG>> Harti Brandt wrote:
EG>> >Nice feature, although it would be nice to align the maximum length with
EG>> >IF-MIB::ifDescr (255 byte + \0). Also I suppose that the field more
EG>> >naturally fits into struct if_data (see net/if.h) given the comment for
EG>> >that struct:
EG>> >
EG>> >/*
EG>> > * Structure describing information about an interface
EG>> > * which may be of interest to management entities.
EG>> > */
EG>>
EG>> The string array should most likely not be part of struct ifnet as that
EG>> would bloat it quite a bit. If it is in there it should be at the end
EG>> of the struct to avoid cache line busting effects.
EG>
EG>Also vote for this. And is it possible to make it a pointer instead
EG>of array? The bloat would be minimal for system with tons of interfaces,
EG>think about large pptp or pppoe server or similar that never would
EG>utilize arrays.

That makes sense. If it is a pointer it should not live in struct ifdata
which can be retrieved via sysctl().

As for access to this field perhaps it makes more sense to use the sysctl
net.link.generic.ifdata subtree. We have already IFDATA_DRIVERNAME there
which returns a string. Could be IFDATA_DESCRIPTION (4). This would
probably be more in line with the management nature of the data. Just a
thought... Would be slightly easier for the SNMP daemon to use...

If must not live in struct ifdata as the size of struct ifdata is part
of the routing socket API. :( There are two bytes avaible in struct
ifdata.

-- Brooks

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