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Re: [Xen-devel] [PATCH] Add support for netconsole driver used on bridge device with VIF attached

On 01/22/2013 11:23 AM, Ian Campbell wrote:
On Mon, 2013-01-21 at 18:00 +0000, yuval.shaia@xxxxxxxxxx wrote:
On 01/21/2013 07:28 PM, Ian Campbell wrote:
On Mon, 2013-01-21 at 17:17 +0000, Yuval Shaia wrote:

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
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?

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?
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 -- | | |
---------- | ----------
| |
| 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.

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?

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.
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.

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


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