selftests: forwarding: Redefine relative_path variable

The following code which is part of lib.sh:
relative_path="${BASH_SOURCE%/*}"
if [[ "$relative_path" == "${BASH_SOURCE}" ]]; then
relative_path="."
fi

reimplements functionality that is part of `dirname`:
$ dirname ""
.

To avoid this duplication, replace "relative_path" by "net_forwarding_dir",
a new variable defined using dirname.

Furthermore, to avoid the potential confusion about what "relative_path" is
about (cwd, test script directory or test library directory), define
"net_forwarding_dir" as the absolute path to net/forwarding/.

Tested-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Benjamin Poirier <bpoirier@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: forwarding: Allow importing dependent libraries

The next patch introduces a new mlxsw-specific test that uses
mirror_gre_lib.sh and mirror_gre_topo_lib.sh.

However when sourcing their own deps, these libraries assume that the
test that's running is in the same directory. That's not the case for
driver-specific tests.

So change the libraries to source their deps through $relative_path.
That variable is set up by lib.sh, which should be imported by the test
in question in any case.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: forwarding: Split mirror_gre_topo_lib.sh

Move generic parts of mirror_gre_topo_lib.sh into a new file
mirror_topo_lib.sh. Reuse the functions in GRE topo, adding the tunnel
devices as necessary.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: forwarding: Add libs for gretap mirror testing

To simplify implementation of mirror-to-gretap tests, extend lib.sh with
several new functions that might potentially be useful more
broadly (although right now the mirroring tests will be the only
client).

Also add mirror_lib.sh with code useful for mirroring tests,
mirror_gre_lib.sh with code specifically useful for mirror-to-gretap
tests, and mirror_gre_topo.sh that primes a given test with a good
baseline topology that the test can then tweak to its liking.

Signed-off-by: Petr Machata <petrm@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>