Re: [PATCH net-next v2 5/6] selftests: drv-net: add primary_rx_redirect support to NetDrvContEnv

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Hardcoding `byteorder='little'` when packing BPF map values breaks the test on big-endian architectures.
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commit 5fba7c06c7ed450ad321c1238af07a759467e25a
Author: Bobby Eshleman <bobbyeshleman@meta.com>

selftests: drv-net: add primary_rx_redirect support to NetDrvContEnv

When sending from a namespace that has access to a netkit device with a
leased queue, the nk primary in the host namespace needs to redirect its
RX to the physical device. This patch adds that redirection bpf program
and teaches the harness to install it.

> diff --git a/tools/testing/selftests/drivers/net/lib/py/env.py b/tools/testing/selftests/drivers/net/lib/py/env.py
> index 24ce122abd9c..d569d01ef791 100644
> --- a/tools/testing/selftests/drivers/net/lib/py/env.py
> +++ b/tools/testing/selftests/drivers/net/lib/py/env.py
[ ... ]
> @@ -505,3 +520,31 @@ class NetDrvContEnv(NetDrvEpEnv):
[ ... ]
> +    def _attach_primary_rx_redirect_bpf(self):
> +        """Attach BPF redirect program on the primary netkit ingress."""
[ ... ]
> +        bss_map_id = self._find_bss_map_id(redirect_prog_id)
> +        phys_ifindex_bytes = self.ifindex.to_bytes(4, byteorder='little')

Does hardcoding byteorder='little' here break the test on big-endian
architectures?

Since .bss maps store integers in native byte order, and BPF programs execute
using the host's native endianness, passing a 4-byte little-endian sequence
on a big-endian system (like s390x) will cause the kernel to interpret the
ifindex backwards.

For example, an ifindex of 1 (01 00 00 00) becomes 16777216 (0x01000000).
This would cause bpf_redirect_neigh() to fail because the byte-swapped ifindex
does not exist on the system, silently dropping all packets.

While a similar pre-existing pattern exists in _attach_bpf(), this duplicates
it into the newly added _attach_primary_rx_redirect_bpf() function.

Could this dynamically use byteorder=sys.byteorder instead so the serialization
matches the host architecture's endianness?

> +        value_hex = ' '.join(f'{b:02x}' for b in phys_ifindex_bytes)
> +        bpftool(f"map update id {bss_map_id} key hex 00 00 00 00 value hex {value_hex}")

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Sashiko AI review · https://sashiko.dev/#/patchset/20260504-tcp-dm-netkit-v2-0-56d52ac72fd4@meta.com?part=5