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From: Laurent Vivier <lvivier@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: passt-dev@passt.top
Subject: Re: [PATCH v8 7/8] vhost-user: add vhost-user
Date: Wed, 16 Oct 2024 12:07:21 +0200	[thread overview]
Message-ID: <45e1f806-7516-41df-a11f-028516bfd513@redhat.com> (raw)
In-Reply-To: <Zw3gHwUiVhTqvFZk@zatzit.fritz.box>

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.

Thanks,
Laurent


  reply	other threads:[~2024-10-16 10:07 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-10-10 12:28 [PATCH v8 0/8] Add vhost-user support to passt. (part 3) Laurent Vivier
2024-10-10 12:28 ` [PATCH v8 1/8] packet: replace struct desc by struct iovec Laurent Vivier
2024-10-10 12:28 ` [PATCH v8 2/8] vhost-user: introduce virtio API Laurent Vivier
2024-10-10 12:28 ` [PATCH v8 3/8] vhost-user: introduce vhost-user API Laurent Vivier
2024-10-10 12:28 ` [PATCH v8 4/8] udp: Prepare udp.c to be shared with vhost-user Laurent Vivier
2024-10-14  4:29   ` David Gibson
2024-10-10 12:28 ` [PATCH v8 5/8] tcp: Export headers functions Laurent Vivier
2024-10-14  4:29   ` David Gibson
2024-10-10 12:29 ` [PATCH v8 6/8] passt: rename tap_sock_init() to tap_backend_init() Laurent Vivier
2024-10-14  4:30   ` David Gibson
2024-10-14 22:38   ` Stefano Brivio
2024-10-10 12:29 ` [PATCH v8 7/8] vhost-user: add vhost-user Laurent Vivier
2024-10-15  3:23   ` David Gibson
2024-10-16 10:07     ` Laurent Vivier [this message]
2024-10-16 16:26       ` Stefano Brivio
2024-10-15 19:54   ` Stefano Brivio
2024-10-16  0:41     ` David Gibson
2024-10-17  0:10       ` Stefano Brivio
2024-10-17 11:25         ` Stefano Brivio
2024-10-17 11:54           ` Laurent Vivier
2024-10-17 17:18           ` Laurent Vivier
2024-10-17 17:25             ` Laurent Vivier
2024-10-17 17:33             ` Stefano Brivio
2024-10-17 21:21               ` Stefano Brivio
2024-10-22 12:59         ` Laurent Vivier
2024-10-22 13:19           ` Stefano Brivio
2024-10-22 18:19             ` Stefano Brivio
2024-10-22 18:22               ` Stefano Brivio
2024-10-23 15:27           ` Laurent Vivier
2024-10-23 16:23             ` Stefano Brivio
2024-10-17  0:10   ` Stefano Brivio
2024-10-17  7:28     ` Laurent Vivier
2024-10-17  8:33       ` Stefano Brivio
2024-11-14 10:20     ` Laurent Vivier
2024-11-14 14:23       ` Stefano Brivio
2024-11-14 15:16         ` Laurent Vivier
2024-11-14 15:38           ` Stefano Brivio
2024-11-14 10:23     ` Laurent Vivier
2024-11-14 14:23       ` Stefano Brivio
2024-11-15  8:30         ` Laurent Vivier
2024-11-15 10:08           ` Stefano Brivio
2024-11-14 10:29     ` Laurent Vivier
2024-11-14 14:23       ` Stefano Brivio
2024-11-15 11:13         ` Laurent Vivier
2024-11-15 11:23           ` Stefano Brivio
2024-10-10 12:29 ` [PATCH v8 8/8] test: Add tests for passt in vhost-user mode Laurent Vivier
2024-10-15  3:40   ` David Gibson
2024-10-15 19:54   ` Stefano Brivio
2024-10-16  8:06     ` Laurent Vivier
2024-10-16  9:47       ` Stefano Brivio

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