Re: [MirageOS-devel] More troubles with tcp on ARM

[Magnus Therning <magnus@xxxxxxxxxxxx>]

On Sat, Apr 11, 2015 at 11:33:40PM +0800, Anil Madhavapeddy wrote:
> On 11 Apr 2015, at 23:13, Magnus Skjegstad <magnus@xxxxx> wrote:
> > 
> > On Fri, 10 Apr 2015, at 05:29, Magnus Therning wrote:
> >> On Thu, Apr 09, 2015 at 10:18:53PM +0200, Magnus Therning wrote:
> >> [...]
> >> I did a little bit more testing of this just now, and found something
> >> surprising.  This is against a VM on ARM:
> >> 
> >> ~~~
> >> % echo thisisalongerstring | ncat -4 192.168.0.33 18080
> >> alongerstring
> >> 
> >> ->
> >> 
> >> tcp: 192.168.0.11:48731
> >> 6 - 
> >> 14 - alongerstring
> >> ~~~
> >> 
> >> and
> >> 
> >> ~~~
> >> % echo thisisalongerstringandthisislongerstill | ncat -4 192.168.0.33
> >> 18080
> >> alongerstringandthisislongerstill
> >> 
> >> ->
> >> 
> >> tcp: 192.168.0.11:48732
> >> 6 - 
> >> 34 - alongerstringandthisislongerstill
> >> ~~~
> >> 
> >> and if I send a string that is shorter than 6 characters (I'm guessing
> >> including the trailing \r\n), then `ncat` hangs and on the ARM I only
> >> see a single line of "length - content":
> >> 
> >> ~~~
> >> tcp: 192.168.0.11:48766
> >> 6 -
> >> ~~~
> >> 
> >> I do wonder where those initial 6 characters go...
> >> 
> > 
> > Hm - I am able to reproduce this. I have a cubieboard and an x86 Xen
> > server connected to the same switch. If I run the unikernel above on the
> > x86 server I can access it remotely and from dom0 without problems. It
> > also works fine if I run the unikernel in Xen on the cubieboard and try
> > to access it from dom0:
> > 
> <snip>
> 
> > I am using tcpip 2.3.1 and mirage-net-xen 1.4.1. 
> 
> Can you bisect backwards a few versions to check if this goes away?
> I'm a few thousands miles away from my Cubies until Tuesday, so can't
> try this out myself.  The usual culprit for such problems is TCP
> offload, but this sounds like more of a physical driver issue.  As
> another datapoint, does a Linux domU VM have networking?

I backed to tcpip 2.3.0 (before the assert "fix") then

1. `ncat` from dom0 works just fine, no assert and full string
   received and returned.
2. `ncat` from my PC triggers the assert, the full string is received
   and returned, but `ncat` hangs.

Is there some pre-packaged ARM Linux guest image to download from
somewhere?

/M

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

Would you go to war without a helmet? Would you drive without the seat
belt?  Then why do you develop software as if shit doesnât happen?
     -- Alberto G ( http://makinggoodsoftware.com/2009/05/12/hdd/ )

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