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README: Add note about --with-verbs-usnic

This option isn't needed on modern distros; add a note to README about
it.

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
(cherry picked from commit 9a8b0d0e18)
Этот коммит содержится в:
Jeff Squyres 2018-08-30 15:05:04 -07:00
родитель 3e842348d1
Коммит 1d0e695bd6

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README
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@ -1020,15 +1020,33 @@ NETWORKING SUPPORT / OPTIONS
configurations.
--with-verbs-usnic
Note that this option is no longer necessary in recent Linux distro
versions. If your Linux distro uses the "rdma-core" package (instead
of a standalone "libibverbs" package), not only do you not need this
option, you shouldn't use it, either. More below.
This option will activate support in Open MPI for disabling a
dire-sounding warning message from libibverbs that Cisco usNIC
devices are not supported (because Cisco usNIC devices are supported
through libfabric, not libibverbs). This libibverbs warning can
also be suppressed by installing the "no op" libusnic_verbs plugin
for libibverbs (see https://github.com/cisco/libusnic_verbs, or
download binaries from cisco.com). This option is disabled by
default because it causes libopen-pal.so to depend on libibverbs.so,
which is undesirable to many downstream packagers.
download binaries from cisco.com).
This option is disabled by default for two reasons:
1. It causes libopen-pal.so to depend on libibverbs.so, which is
undesirable to many downstream packagers.
2. As mentioned above, recent versions of the libibverbs library
(included in the "rdma-core" package) do not have the bug that
will emit dire-sounding warnings about usnic devices. Indeed,
the --with-verbs-usnic option will enable code in Open MPI that
is actually incompatible with rdma-core (i.e., cause Open MPI to
fail to compile).
If you enable --with-verbs-usnic and your system uses the rdma-core
package, configure will safely abort with a helpful message telling
you that you should not use --with-verbs-usnic.
--with-usnic
Abort configure if Cisco usNIC support cannot be built.