Re: [MirageOS-devel] mirage-www on xen and networking (on ARM)

[David Scott <scott.dj@xxxxxxxxx>]

On Sun, Mar 29, 2015 at 5:02 PM, Magnus Therning <magnus@xxxxxxxxxxxx> wrote:

I've finally managed to set up an ARM system that can compile
successfully (based on the pre-built image with swap added and an NTP
client installed). Compiling for unix now works perfectly fine,
albeit a bit slow.

The next step was to get mirage-www into a xen image. I've
succesfully built and started the following two configurations:

  MODE=xen FS=crunch NET=direct DHCP=true PORT=80
  MODE=xen FS=crunch DEPLOY=true ADDR=192.168.0.21 MASK=255.255.255.0 GWS=192.168.0.1 PORT=80

In both cases I've modified www.xl to contain

  vif = [ 'bridge=xenbr0' ]

In both cases the VM comes up just fine, when using DCHP it gets an IP
without issues. Then, when sitting there waiting for a connection I
get this on the console:

  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed

Assuming you're using the v2.3.0 release (IIRC v2.4.0 hasn't been merged yet), then this is the assert:

 let input t ~tcp ~udp ~default buf =

  (* buf pointers to start of IPv4 header here *)

  let ihl = (Wire_structs.Ipv4_wire.get_ipv4_hlen_version buf land 0xf) * 4 in

  let src = "" (Wire_structs.Ipv4_wire.get_ipv4_src buf) in

  let dst = Ipaddr.V4.of_int32 (Wire_structs.Ipv4_wire.get_ipv4_dst buf) in

  let payload_len = Wire_structs.Ipv4_wire.get_ipv4_len buf - ihl in

  (* XXX this will raise exception for 0-length payload *)

  let hdr, data = "" buf ihl in

  assert (Cstruct.len data = "">

  let proto = Wire_structs.Ipv4_wire.get_ipv4_proto buf in

  match Wire_structs.Ipv4_wire.int_to_protocol proto with

  | Some `ICMP -> icmp_input t src hdr data

  | Some `TCP Â-> tcp ~src ~dst data

  | Some `UDP Â-> udp ~src ~dst data

  | None    -> default ~proto ~src ~dst data

So it looks like you're receiving truncated IP frames. It would be helpful to know what the frames actually are-- could you do something like:

git clone git://github.com/mirage/mirage-tcpip

cd mirage-tcpip

git checkout v2.3.0

perhaps change the assert into something like

if Cstruct.len data <> payload_len then begin

 printf "argh, it's all broken! len = %d payload_len = %d\n" (Cstruct.len data) payload_len;

 Cstruct.hexdump buf;

end

(quoting the Cstruct manual:

Â" when the going gets tough, the tough hexdump their cstructs

  and peer at it until the bug disappears. This will directly

  prettyprint the contents of the cstruct to the standard output. ")

opam pin add tcpip .

.. and then rebuild your app with the new code.

[ snip ]Â

  DHCP: offer received
            IPv4: 192.168.0.21
                     Netmask: 255.255.255.0
                                Gateways: [192.168.0.1]
  Âsg:true gso_tcpv4:true rx_copy:true rx_flip:false smart_poll:false
  ARP: sending gratuitous from 192.168.0.21
  DHCP offer received and bound to 192.168.0.21 nm 255.255.255.0 gw [192.168.0.1]

It's obviously not all bad, since some networking is working!

Â

  Manager: configuration done
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  ARP responding to: who-has 192.168.0.21?
  ARP: transmitting probe -> 192.168.0.11
  ARP: updating 192.168.0.11 -> 00:c2:c6:0f:72:dd

When making a request to 192.168.0.21 I get a bit of a response, but not a full
one and the console is filled with stuff like this:

  200 GET /
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  TCP retransmission on timer seq = 452908524
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  TCP retransmission on timer seq = 452908524
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  TCP retransmission on timer seq = 452908524
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  TCP retransmission on timer seq = 452908524
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  TCP retransmission on timer seq = 452908524
  RX exn File "lib/ipv4.ml", line 181, characters 4-10: Assertion failed
  ARP responding to: who-has 192.168.0.21?

Clearly I'm doing something wrong here, but what? Any and all suggestions are
welcome.

I don't think the assert failures are your fault ;-)

Cheers,

Dave

Â

/M

--
Magnus Therning           OpenPGP: 0xAB4DFBA4
email: magnus@xxxxxxxxxxxx Âjabber: magnus@xxxxxxxxxxxx
twitter: magthe       Âhttp://therning.org/magnus

The ultimate goal of all computer science is the program. The
performance of programs was once the noblest function of computer
science, and computer science was indispensable to great programs.
Today, programming and computer science exist in complacent isolation,
and can be [rescued only] by conscious coÃperation and collaboration
of all programmers.

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--

Dave Scott

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