On Tuesday 22 January 2013 11:23:32 am Ian Campbell wrote:

On Mon, 2013-01-21 at 18:00 +0000, yuval.shaia@oracle.com wrote:

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On 01/21/2013 07:28 PM, Ian Campbell wrote:

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On Mon, 2013-01-21 at 17:17 +0000, Yuval Shaia wrote:

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When starting a VM which has virtual interface attached to the same
bridge (i.e vif = [type=netfront,bridge=xenbr0'] in vm.cfg) which is
used for netconsole the
following message appears (after about 60 seconds) and VM creation
operation fails.
       Error: Device 0 (vif) could not be connected. Hotplug scripts
not working.

I'm not sure how this can relate netconsole since this happens before
the guest even runs, doesn't it?

Running the same scenario without netconsole runs smoothly.

But why? I can't make sense of your scenario and therefore cannot
explain why this patch would make any difference. Perhaps your patch is
just papering over some other issue?

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As i see it, netconsole driver requires ndo_poll_controller from the
device's controlling driver (function __netpoll_setup in
net/core/netpoll.c), a thing that is not supported currently in
xen_netback driver which is the driver that runs on dom0 and serve
VM's virtual interface.

Which domain is using netconsole? Is it dom0 or domU? What parameters
do you give it?

dom0.
parameters: netconsole=1111@src-ip/xenbr0,2002@dst-ip/dst-mac

You give these parameters to dom0 so that dom0's own logs are sent to
some other host?

Are dst-ip and dst-mac a domain on the same host or are they some offbox
logging service?

Sorry, my mistake, i should have attach network setup at first.
Anyway, here is my setup:
----------                       ----------
| Host A |--bond0--->|           | Host B |
|--------|           |--xenbr0   |        |
| VM A1  |--vif1.0-->|     |     |        |
----------                 |     ----------
                           |         |
                           V         V
---------------------------------------------
|                   LAN                     |
---------------------------------------------

I'm using netconsole to capture logs from  Host-A and send them to Host-B.
Host-A and Host-B are separate hosts (running XEN) which are  connected to the 
same LAN.
src-ip is Host-A address.
dst-ip/mac is Host-B address.

I can see why the *bridge* device might need an ndo_poll_controller hook
in this setup but I can't see any reason why the netback device would
need one.

Please note that without netback driver netconsole runs fine, i.e before trying 
to create VM which attached to the bridge.

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I assume it is the domU but if that's the case I don't see why a
netback rather than netfront patch would be required.

Or is dom0 doing netconsole where the log receiver is a domU?

Log received at dom0 as output of xm cr vm.cfg command.
netconsole is used on dom0 to monitor its log

Are you now saying that logging goes from domU to dom0? Which is it?

netback comes to play as soon as i'm attaching virtual interface to a bridge 
and since this bridge is under netconsole monitoring the function is 
triggered. Up to that point there is no issue getting logs in Host-B so i 
assume the problem is not with the bridge driver.

In this scenario there is really no reason I can see that netback would
need an ndo_poll_controller hook -- that would be needed in the domU in
the netfront driver.

Please can you explain the exact code path which results in this new
hook being called.

init_netconsole() in netconsole.c -> alloc_param_target() -> netpoll_setup() 
in netpoll.c -> __netpoll_setup() which check if ndo_poll_controller() 
operation is supported.

BTW looking at the patch as it is any use of this hook should be wrapped
in CONFIG_NET_POLL_CONTROLLER.

Ian.