svn commit: r192612 - head/sys/netinet

Julian Elischer julian at
Sat May 23 10:01:13 UTC 2009

Robert Watson wrote:
> On Fri, 22 May 2009, Bjoern A. Zeeb wrote:
>> On Fri, 22 May 2009, Bjoern A. Zeeb wrote:
>>> Author: bz
>>> Date: Fri May 22 23:03:15 2009
>>> New Revision: 192612
>>> URL:
>>> Log:
>>>  If including vnet.h one has to include opt_route.h as well. This is
>>>  because struct vnet_net holds the rt_tables[][] for MRT and array size
>>>  is compile time dependent.  If you had ROUTETABLES set to >1 after
>>>  r192011 V_loif was pointing into nonsense leading to strange results
>>>  or even panics for some people.
>>>  Reviewed by:    mz
>> Thanks to everyone who helped to debug this!
> This sounds like the sort of bug that will recur easily in the future, 
> as the double array based on configurable dimensions is not a very 
> robust structure in C.  Is there something we can do to make this more 
> robust?  For example, add assertions around consumers that appropriate 
> includes are present in those consumers?  Also, given that it's a 
> compile-time option, rt_tables should probably be indirected to so that 
> there isn't an issue with modules compiled with different kernel 
> options?  Especially network device drivers/modules that may need to use 
> vnet and be distributed as binary ko's?

the approach taken in freebsd 7 and 6 for MRT was to allow for 100% 
backwards compatibility.. (A one dimensional array is just a 
degenerate case of a 2 dimensional array), however in 8.0 I can break 
the ABI so I'm tying to design a better way of doing this, possibly by 
moving to an array of pointers which in the MRT case would point to a 
vector of items but in the simple case to only a single item.
Together with a method and some data in the domain structure, this
might lead to a more flexible method that does not require pre-sized 

       ------ protocol family number----
!    [0][0][0][H][0][H][0][H][0][0][0][0]
fib  [0][0][0][H][0][0][0][H][0][0][0][0]
!    [0][0][0][H][0][0][0][H][0][0][0][0]
!    [0][0][0][H][0][0][0][H][0][0][0][0]

where 'H' is a pointer to a fib 'tree' head

       ------ protocol family number----
               |     |     |
               v     v     v
              [H]   [H]   [H]
              [H]         [H]
              [H]         [H]
              [H]         [H]

where [H] is a fib head pointer,
and the domain struct for each protcol says show many elements
there are for that protocol family in the vector.

the end result is that what is eventually virtualised is fixed in size.

   rnh = V_rt_tables[fib][AF_INET]
   rnh = (*V_rt_tables[AF_INET])[fib]  where fib has previously been 
constrained to 0 in protocols where multiple fibs are not supported,
and to 'maxfib(protocol)' otherwise.

I'm open to other suggestions as well of course.
but remember that netstat needs to be able to follow
whatever we do on core dumps.

> Robert N M Watson
> Computer Laboratory
> University of Cambridge

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