possible for a panic to occur if BPF is in use on the interface at the
time of the call to if_detach. This happens because BPF maintains pointers
to the struct ifnet describing the interface, which is freed by if_detach.
To correct this problem, a new call, bpfdetach, is introduced. bpfdetach
locates BPF descriptor references to the interface, and NULLs them. Other
BPF code is modified so that discovery of a NULL interface results in
ENXIO (already implemented for some calls). Processes blocked on a BPF
call will also be woken up so that they can receive ENXIO.
Interface drivers that invoke bpfattach and if_detach must be modified to
also call bpfattach(ifp) before calling if_detach(ifp). This is relevant
for buses that support hot removal, such as pccard and usb. Patches to
all effected devices will not be committed, only to if_wi.c, due to
testing limitations. To reproduce the crash, load up tcpdump on you
favorite pccard ethernet card, and then eject the card. As some pccard
drivers do not invoke if_detach(ifp), this bug will not manifest itself
for those drivers.
Reviewed by: wes
de5d99354f