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

On 17/10/2024 13:25, Stefano Brivio wrote:
...
  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 this kernel on my laptop... but I need to reboot.
I will dig into this.

Thanks,
Laurent