Re: [PATCH v8 7/8] vhost-user: add vhost-user

17 Oct 2024


      On 17/10/2024 19:18, Laurent Vivier wrote:
...
On 17/10/2024 13:25, Stefano Brivio wrote:
...
On Thu, 17 Oct 2024 02:10:31 +0200
Stefano Brivio  wrote:
...
On Wed, 16 Oct 2024 11:41:34 +1100
David Gibson  wrote:
...
On Tue, Oct 15, 2024 at 09:54:38PM +0200, Stefano Brivio wrote:
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[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".
strace gives me:

socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC, IPPROTO_TCP) = 73
setsockopt(73, SOL_SOCKET, SO_PEEK_OFF, [0], 4) = 0
socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC, IPPROTO_TCP) = 73
setsockopt(73, SOL_SOCKET, SO_PEEK_OFF, [0], 4) = -1 EOPNOTSUPP (Operation not supported)

Thanks,
Laurent