On Thu, 17 Oct 2024 02:10:31 +0200
Stefano Brivio <sbrivio(a)redhat.com> wrote:
On Wed, 16 Oct 2024 11:41:34 +1100
David Gibson <david(a)gibson.dropbear.id.au> wrote:
> On Tue, Oct 15, 2024 at 09:54:38PM +0200, Stefano Brivio wrote:
>> [Still partial review]
> [snip]
>>> + if (peek_offset_cap)
>>> + already_sent = 0;
>>> +
>>> + iov_vu[0].iov_base = tcp_buf_discard;
>>> + iov_vu[0].iov_len = already_sent;
>>
>> I think I had a similar comment to a previous revision. Now, I haven't
>> tested this (yet) on a kernel with support for SO_PEEK_OFF on TCP, but
>> I think this should eventually follow the same logic as the (updated)
>> tcp_buf_data_from_sock(): we should use tcp_buf_discard only if
>> (!peek_offset_cap).
>>
>> It's fine to always initialise VIRTQUEUE_MAX_SIZE iov_vu items,
>> starting from 1, for simplicity. But I'm not sure if it's safe to pass
a
>> zero iov_len if (peek_offset_cap).
>
>> I'll test that (unless you already did) -- if it works, we can fix this
>> up later as well.
>
> I believe I tested it at some point, and I think we're already using
> it somewhere.
I tested it again just to be sure on a recent net.git kernel: sometimes
the first test in passt_vu_in_ns/tcp, "TCP/IPv4: host to guest: big
transfer" hangs on my setup, sometimes it's the "TCP/IPv4: ns to guest
(using loopback address): big transfer" test instead.
I can reproduce at least one of the two issues consistently (tests
stopped 5 times out of 5).
The socat client completes the transfer, the server is still waiting
for something. I haven't taken captures yet or tried to re-send from
the client.
...Laurent, let me know if I should dig into this any further.
For reference, the kernel commit introducing SO_PEEK_OFF support for TCP
on IPv6 is be9a4fb831b8 ("tcp: add SO_PEEK_OFF socket option tor
TCPv6"). Without that commit, passt won't set peek_offset_cap.
It was added in 6.11-rc5, so it's part of kernel-6.11.3-200.fc40 (latest
stable kernel) for Fedora 40. passt will print "SO_PEEK_OFF supported"
if you run it with -d -f.
I have kernel 6.11.3-200.fc40.x86_64 but the message is "SO_PEEK_OFF not
supported".
Any idea?