On 15/10/2024 05:23, David Gibson wrote:
+/**
+ * tcp_vu_update_check() - Calculate TCP checksum
+ * @tapside: Address information for one side of the flow
+ * @iov: Pointer to the array of IO vectors
+ * @iov_used: Length of the array
+ */
+static void tcp_vu_update_check(const struct flowside *tapside,
+ struct iovec *iov, int iov_used)
AFAICT this is only used for the
pcap path. Rather than filling in
the checksum at a different point from normal, I think it would be
easier to just clear the no_tcp_csum flag when pcap is enabled. That
would, AFAICT, remove the need for this function entirely.
To do that is a little bit complicated because we need to pass the iov array to
tcp_fill_headers4()/tcp_fill_headers6() to be able to compute the checksum of the TCP
part.
In tcp_buf, the TCP header and TCP payload are in the same iovec but with tcp_vu they can
be split on several iovecs. And if we provide the iovec , theoretically we should not
provide the TAP, IP and TCP headers via the parameters as they are in the iovec, but for
tcp_buf they have one iovec each, and with tcp_vu they are probably all in the same iovec
(the first one). So, again, it can be complicated to extract headers to update them.
In conclusion, I update the checksum only for VU and in the case of pcap because it is
simpler (the same logic applies for udp_update_hdr4()/udp_update_hdr6()).
I'm open to any suggestion that could do the checksum in
udp_update_hdr4()/udp_update_hdr6() (I agree with you, it should be the place to do it)
but I don't see an easy and nice way to implement it.