Re: [PATCH v11 5/9] flow: add MAC address of LAN local remote hosts to flow

On Tue, Sep 30, 2025 at 11:29:32PM +0200, Stefano Brivio wrote:

On Sat, 27 Sep 2025 15:25:18 -0400 Jon Maloy wrote:

...

When communicating with remote hosts on the local network, some guest applications want to see the real MAC address of that host instead of PASST/PASTA's own tap address. The flow_common structure is a convenient location for storing that address, so we do that in this commit.

Note that we don´t add actual usage of this address here, that will be done in later commits.

Signed-off-by: Jon Maloy Reviewed-by: David Gibson

--- v3: - Moved the remote host macaddress from struct flowside to struct flow_common. I chose to call it 'omac' as suggested by David, although in my understanding the correct name would be 'emac'. (In general I find the address naming scheme confusing.) - Adapted to new signature of function nl_mac_get(), now passing it the index of the template interface. v4: - Renamed flow_commeon->omac to flow_common->tap_omac to make is role in the code clearer v5: - Modified the criteria for ARP/NDP table lookup like in the previous commits. - Removed the PIF_TAP lookup case, as David suggested, and did instead give the flow->tap_omac field a value marking it as non-initialized. - Calling the cache table instead of netlink for ARP/NDP lookup. - Unconditionally using the potentially translated IP address in the lookup, instead of only if NAT really was applied. v6: - Using MAC_ZERO instead of own definitions --- flow.c | 2 ++ flow.h | 2 ++ 2 files changed, 4 insertions(+)

diff --git a/flow.c b/flow.c index feefda3..510f3c5 100644 --- a/flow.c +++ b/flow.c @@ -449,6 +449,7 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,

switch (f->pif[INISIDE]) { case PIF_TAP: + memcpy(f->tap_omac, MAC_ZERO, ETH_ALEN);

I see in the next patch that this is needed as an invalid value for f->tap_omac, but MAC_ZERO is actually a valid, usable MAC address.

Good point, I'd forgotten about that.

I guess we should use ff:ff:ff:ff:ff:ff, instead, as MAC_ONES, or MAC_UNSPEC.

We already have MAC_BROADCAST. -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson