Xen users - Oct 2007 - How to tell which tapX interface belongs to which domain...

I''ve put together a script to get the traffic counters for a given vm
interface (eg "vmif_traffic <domain> <if index>") and it
works great
except when the interface backend is ioemu, because all the traffic goes
through the tapX interface instead of the vif interface.

Is there a way to tell what the tapX interface is for a given domain''s
interface?

Thanks

James

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On Mon, Oct 08, 2007 at 03:36:39PM +1000, James Harper
wrote:
> I''ve put together a script to get the traffic counters for a given
vm
> interface (eg "vmif_traffic <domain> <if index>") and
it works great
> except when the interface backend is ioemu, because all the traffic goes
> through the tapX interface instead of the vif interface.
I''m just doing the same, and besides not getting i/o yet i also miss
the
number of tap-interfaces, would fit into ''xm list -l
<domain>'' output.
An idea to get the mapping could be to have a look on what tap-interfaces
are in use bevore domain-creation and after, the interfaces in use now
are the ones belonging to the domain.

Had a look at the filehandles that are open for /dev/net/tun and the 
qemu-dm processed, and at the logfiles, without better hints.


Christian

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> On Mon, Oct 08, 2007 at 03:36:39PM +1000, James Harper wrote:
> > I''ve put together a script to get the traffic counters for a
given
vm
> > interface (eg "vmif_traffic <domain> <if
index>") and it works great
> > except when the interface backend is ioemu, because all the traffic
goes
> > through the tapX interface instead of the vif interface.
> 
> I''m just doing the same, and besides not getting i/o yet i also
miss
the
> number of tap-interfaces, would fit into ''xm list -l
<domain>'' output.
> An idea to get the mapping could be to have a look on what
tap-interfaces
> are in use bevore domain-creation and after, the interfaces in use now
> are the ones belonging to the domain.
> 
> Had a look at the filehandles that are open for /dev/net/tun and the
> qemu-dm processed, and at the logfiles, without better hints.
I noticed that when I do a ''brctl show'', the tap interface is
on the
line before the vif interface, so I made use of that. Hopefully it''s
always true!

James

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212-798
> -----Original Message-----
> From: James Harper
> Sent: Tuesday, 9 October 2007 12:00
> To: ''Christian Horn''
> Cc: xen-users@lists.xensource.com
> Subject: RE: [Xen-users] How to tell which tapX interface belongs to
which
> domain...
> 
> > On Mon, Oct 08, 2007 at 03:36:39PM +1000, James Harper wrote:
> > > I''ve put together a script to get the traffic counters
for a given
vm
> > > interface (eg "vmif_traffic <domain> <if
index>") and it works
great
> > > except when the interface backend is ioemu, because all the
traffic
> goes
> > > through the tapX interface instead of the vif interface.
> >
> > I''m just doing the same, and besides not getting i/o yet i
also miss
the
> > number of tap-interfaces, would fit into ''xm list -l
<domain>''
output.
> > An idea to get the mapping could be to have a look on what tap-
> interfaces
> > are in use bevore domain-creation and after, the interfaces in use
now
> > are the ones belonging to the domain.
> >
> > Had a look at the filehandles that are open for /dev/net/tun and the
> > qemu-dm processed, and at the logfiles, without better hints.
> 
> I noticed that when I do a ''brctl show'', the tap
interface is on the
line
> before the vif interface, so I made use of that. Hopefully it''s
always
> true!
> 
> James
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Err... sorry... I hit reply to the wrong email :)
> -----Original Message-----
> From: James Harper
> Sent: Tuesday, 9 October 2007 12:13
> To: James Harper; Christian Horn
> Cc: xen-users@lists.xensource.com
> Subject: RE: [Xen-users] How to tell which tapX interface belongs to
which
> domain...
> 
> 212-798
> 
> > -----Original Message-----
> > From: James Harper
> > Sent: Tuesday, 9 October 2007 12:00
> > To: ''Christian Horn''
> > Cc: xen-users@lists.xensource.com
> > Subject: RE: [Xen-users] How to tell which tapX interface belongs to
> which
> > domain...
> >
> > > On Mon, Oct 08, 2007 at 03:36:39PM +1000, James Harper wrote:
> > > > I''ve put together a script to get the traffic
counters for a
given
> vm
> > > > interface (eg "vmif_traffic <domain> <if
index>") and it works
great
> > > > except when the interface backend is ioemu, because all the
traffic
> > goes
> > > > through the tapX interface instead of the vif interface.
> > >
> > > I''m just doing the same, and besides not getting i/o yet
i also
miss
> the
> > > number of tap-interfaces, would fit into ''xm list -l
<domain>''
output.
> > > An idea to get the mapping could be to have a look on what tap-
> > interfaces
> > > are in use bevore domain-creation and after, the interfaces in
use
now
> > > are the ones belonging to the domain.
> > >
> > > Had a look at the filehandles that are open for /dev/net/tun and
the
> > > qemu-dm processed, and at the logfiles, without better hints.
> >
> > I noticed that when I do a ''brctl show'', the tap
interface is on the
> line
> > before the vif interface, so I made use of that. Hopefully
it''s
always
> > true!
> >
> > James
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On Tue, Oct 09, 2007 at 12:00:29PM +1000, James Harper
wrote:
> 
> I noticed that when I do a ''brctl show'', the tap
interface is on the
> line before the vif interface, so I made use of that. Hopefully
it''s
> always true!
Also seen that, but how do you conclude from that to which domU the
tap-device belongs?

I think i found something usable:


- ping the ip of the domU on the tap-interface you want to identify,
i.e. ''ping -c2 ch_hvmadm''
I also have the mac of my domU on that interface from the xen-config,
its aa:00:00:00:00:03 in this case.


- from the ping we have the mac in the arp-cache, and 
''brctl showmacs xenadm0'' shows the macs known on that bridge:
   -----------
   port no mac addr             is local?  ageing timer
     2     00:03:d2:11:0d:fb    no            1.57
   [....]
     4     6e:14:9d:77:3a:cd    yes            0.00
     4     aa:00:00:00:00:03    no          138.21
     1     fe:ff:ff:ff:ff:ff    yes            0.00
   -----------


- the ''port'' column of my well-known mac is important, its 4.
Issuing ''brctl show'' i get the connected tap-interface on the
4th line:
   -----------
   bridge name     bridge id       STP enabled     interfaces
   xenadm0         8000.6e149d773acd       no      vif0.0
                                                   peth0
                                                   vif1.0
                                                   tap0
                                                   vif17.0
   [.....]
   -----------

So now for implementing it into my perl/rrdtool scripts..


Christian

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> On Tue, Oct 09, 2007 at 12:00:29PM +1000, James Harper wrote:
> >
> > I noticed that when I do a ''brctl show'', the tap
interface is on the
> > line before the vif interface, so I made use of that. Hopefully
it''s
> > always true!
> 
> Also seen that, but how do you conclude from that to which domU the
> tap-device belongs?
> 
You can get that from xenstore.

My scripts are (excuse the line feeds):

1. Generic interface script (parameter is interface name):

"
#!/bin/sh

cat /proc/net/dev | egrep "^[ ]*$1:" | sed ''s/[
]*[^:][^:]*://'' | while
read rxbytes rxpackets rxerrs rxdrop rxfifo rxframe rxcompressed
rxmulticast txbytes txpackets txerrs txdrop txfifo txcolls txcarrier
txcompressed
do
  echo $rxbytes
  echo $txbytes
  uptime | cut -c14- | sed ''s/,  .*//''
  hostname
done
"

2. DomU interface script (parameters are domain name and interface
index)

"
#!/bin/sh

domname=$1
vifindex=$2

/usr/sbin/xenstore-list /local/domain | while read domid
do
  name=`/usr/sbin/xenstore-read /local/domain/$domid/name`

  if [ "$name" = "$domname" ]
  then
    type=`/usr/sbin/xenstore-read
/local/domain/0/backend/vif/$domid/$vifindex/type 2>/dev/null`
    if [ "$type" = "ioemu" ]
    then
      if=`/usr/sbin/brctl show | sed ''s/.*[      ]//'' | egrep
-B 1
"^vif$domid.$vifindex" | head -1`
    else
      if=vif$domid.$vifindex
    fi
    /usr/local/bin/if_traffic $if
    exit
  fi
done
"

The only problem I can see with the second script, is that I don''t
think
you can rely on the ''ioemu'' text being present in that key, on
another
machine it is blank. It probably comes from the config script...

James

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On Tue, Oct 09, 2007 at 03:35:47PM +1000, James Harper
wrote:
> 
> You can get that from xenstore.
> 
> [..]
>
> /usr/sbin/xenstore-list /local/domain | while read domid
> do
>   name=`/usr/sbin/xenstore-read /local/domain/$domid/name`
> 
>   if [ "$name" = "$domname" ]
>   then
>     type=`/usr/sbin/xenstore-read
> /local/domain/0/backend/vif/$domid/$vifindex/type 2>/dev/null`
>     if [ "$type" = "ioemu" ]
>     then
>       if=`/usr/sbin/brctl show | sed ''s/.*[      ]//'' |
egrep -B 1
> "^vif$domid.$vifindex" | head -1`
>     else
>       if=vif$domid.$vifindex
>     fi
>     /usr/local/bin/if_traffic $if
>     exit
>   fi
> done
> "
Works great, thanks.
And /proc/net/dev gives me all values at ones, till today i read single
files under /sys for each interface.

> The only problem I can see with the second script, is that I don''t
think
> you can rely on the ''ioemu'' text being present in that
key, on another
> machine it is blank. It probably comes from the config script...
My perl-script here returns different errorcodes for ''value could not
be read'' (=para-domU) and ''error executing
xenstore-read'' at all.


Christian

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On October 9, 2007, Christian Horn wrote:
> - from the ping we have the mac in the arp-cache, and
> ''brctl showmacs xenadm0'' shows the macs known on that
bridge:
>    -----------
>    port no mac addr             is local?  ageing timer
>      2     00:03:d2:11:0d:fb    no            1.57
>    [....]
>      4     6e:14:9d:77:3a:cd    yes            0.00
>      4     aa:00:00:00:00:03    no          138.21
>      1     fe:ff:ff:ff:ff:ff    yes            0.00
>    -----------
>
>
> - the ''port'' column of my well-known mac is important,
its 4.
> Issuing ''brctl show'' i get the connected tap-interface on
the
> 4th line:
>    -----------
>    bridge name     bridge id       STP enabled     interfaces
>    xenadm0         8000.6e149d773acd       no      vif0.0
>                                                    peth0
>                                                    vif1.0
>                                                    tap0
>                                                    vif17.0
>    [.....]
>    -----------
One thing to watch out for: While the port number gets incremented for each 
device you add to the bridge, any devices that are removed leave a hole. If 
you remove vif1.0 from the bridge above, tap0 will still be port 4, but it 
will be the third entry in ''brctl show'' output. If you
start/stop instances a
lot, you will run into that problem.

Unfortunately, the true mapping is not exposed to userspace. At least I could 
not find it in linux/if_bridge.h.

-- 
James Oakley
jfunk@funktronics.ca

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