0715802f52 missed that there is a call
to a common/verbs_usnic symbol in the common/verbs component. This
call needs to be compiled out when the common/verbs_usnic component is
not built.
This component is a workaround to a bug in libibverbs that prints a
dire warning that usNIC devices are not supported (of course not --
usNIC devices provide functionality through libfabric, not
libibverbs). This component was written before a better workaround
was created: a "no op" libibverbs plugin for usNIC devices
(https://github.com/cisco/libusnic_verbs, and is also available in
binary form on cisco.com).
Hence, this component no longer builds by default. It's still
available if a user specifically asks for it (e.g., if they do not
want to install the "no op" libibverbs plugin), but it's not the
default. This component also has the side-effect of making
libopen-pal.so depend on libibverbs.so, which can be annoying for
packagers (which is another reason it isn't built by default any
more).
Move the fake usnic IBV provider out of common/verbs and into a new
common/verbs_usnic component that is always statically linked into
libopen-pal. The fake provider is registered with libibverbs at run
time, but there is no *un*register IBV API. Hence, we can't let the
code containing this provider be dlclosed -- which means it needs to
be statically linked into libopen-pal.
Fixesopen-mpi/ompi#1060.
