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: http://svn.freebsd.org/changeset/base/192612
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
arrays.
7.x:
------ 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
8.0
------ protocol family number----
[0][0][0][.][0][.][0][.][0][0][0][0]
| | |
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.
thus
rnh = V_rt_tables[fib][AF_INET]
becomes
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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