On Sun, 29 Jan 2006, Julian Elischer wrote:
Note that with these changes, these drivers now depend on locking the
global
if_addr_mtx, so binary modules of these drivers will not work on 5.4 or
earlier releases.
Is the converse true?
i.e. can older binaries (e.g. from 5.4) work on 5.5?
this is a "must"
Yes. The "problem" is that modules using the new locking will reference a new
global symbol, if_addr_mtx. Old modules will continue to load fine, and
continue to not have locking around their manipulation of the multicast
address lists, so will not work worse than they did before. New modules build
from our kernel tree will have the new symbol reference -- vendor drivers that
don't have the locking but are built on new systems will continue to work fine
on old kernels, but it is desirable for vendors to add the locking to avoid
race conditions in multicast address management, which can be observed in the
wild when using multicast moderately heavily.
The version of multicast address locking merged to RELENG_5 by Ed is actually
a fairly modified version of the code I originally committed to HEAD -- I
added an if_addr_mtx field to struct ifnet, which is used for synchronizing
per-ifnet address lists. We didn't want to modify struct ifnet in RELENG_5,
so he added a global mutex which is accessed by the macros instead, giving
driver source compatibility with RELENG_6 and HEAD, but avoiding changes to
struct ifnet.
I.e., I think all is fine.
Robert N M Watson
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