Help understanding this part of the network config code?

[Michael DeHaan]

I recently made a change so that if a system in Cobbler has multiple 
interfaces but no details about those interfaces, the kickstart is still 
valid -- that is to say, it's trivially easy to make a virtual machine 
again that has no MAC, IP, or hostname assignments if someone wants.

However, when I create such a system, I get a network config post 
section that I don't /quite/ understand.  As I understand it this code 
is intended to reorder the NICs such that they are in the right order 
(assumed ok) and optionally set up bonding and vlan information (assumed ok)

Here's what I get:

mkdir /etc/sysconfig/network-scripts/cobbler
cp /etc/sysconfig/network-scripts/ifcfg-lo 
/etc/sysconfig/network-scripts/cobbler/
#  Start eth1
sed -i "s/eth0/eth1/" /etc/modprobe.conf
(
grep -v "DEVICE=" /etc/sysconfig/network-scripts/ifcfg-eth0
echo "DEVICE=eth1"
) > /etc/sysconfig/network-scripts/cobbler/ifcfg-eth1
#  End eth1
#  Start eth0
sed -i "s/eth1/eth0/" /etc/modprobe.conf
(
grep -v "DEVICE=" /etc/sysconfig/network-scripts/ifcfg-eth1
echo "DEVICE=eth0"
) > /etc/sysconfig/network-scripts/cobbler/ifcfg-eth0
#  End eth0
rm -f /etc/sysconfig/network-scripts/ifcfg-*
mv /etc/sysconfig/network-scripts/cobbler/* /etc/sysconfig/network-scripts/
rm -r /etc/sysconfig/network-scripts/cobbler
cat /etc/modprobe.conf.cobbler >> /etc/modprobe.conf
rm -f /etc/modprobe.conf.cobbler
# End post_install_network_config generated code


 From the above, the two sed lines look redundant.   What are they 
intended to do?

It looks like they change eth0 to eth1 and then eth1 to eth0, but this 
doesn't seme to make since to me.

--Michael

[James Cammarata]

>   From the above, the two sed lines look redundant.   What are they
>  intended to do?
>  
>  It looks like they change eth0 to eth1 and then eth1 to eth0, but this
>  doesn't seme to make since to me. 
Yeah that swaps eth0/eth1... I am not sure of the reason why.

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[Jeff Schroeder]

On Mon, Dec 8, 2008 at 2:05 PM, Michael DeHaan <mdehaan(a)redhat.com&gt; wrote:
>  I recently made a change so that if a system in Cobbler has multiple
>  interfaces but no details about those interfaces, the kickstart is still
>  valid -- that is to say, it's trivially easy to make a virtual machine
>  again that has no MAC, IP, or hostname assignments if someone wants.
>
>  However, when I create such a system, I get a network config post
>  section that I don't /quite/ understand.  As I understand it this code
>  is intended to reorder the NICs such that they are in the right order
>  (assumed ok) and optionally set up bonding and vlan information (assumed ok)
>
>  Here's what I get:
>
>  mkdir /etc/sysconfig/network-scripts/cobbler
>  cp /etc/sysconfig/network-scripts/ifcfg-lo
>  /etc/sysconfig/network-scripts/cobbler/
>  #  Start eth1
>  sed -i "s/eth0/eth1/" /etc/modprobe.conf
>  (
>  grep -v "DEVICE=" /etc/sysconfig/network-scripts/ifcfg-eth0
>  echo "DEVICE=eth1"
>  ) > /etc/sysconfig/network-scripts/cobbler/ifcfg-eth1
>  #  End eth1
>  #  Start eth0
>  sed -i "s/eth1/eth0/" /etc/modprobe.conf
>  (
>  grep -v "DEVICE=" /etc/sysconfig/network-scripts/ifcfg-eth1
>  echo "DEVICE=eth0"
>  ) > /etc/sysconfig/network-scripts/cobbler/ifcfg-eth0
>  #  End eth0
>  rm -f /etc/sysconfig/network-scripts/ifcfg-*
>  mv /etc/sysconfig/network-scripts/cobbler/* /etc/sysconfig/network-scripts/
>  rm -r /etc/sysconfig/network-scripts/cobbler
>  cat /etc/modprobe.conf.cobbler >> /etc/modprobe.conf
>  rm -f /etc/modprobe.conf.cobbler
>  # End post_install_network_config generated code
>
>
>   From the above, the two sed lines look redundant.   What are they
>  intended to do? 
My guess would be it is a cheap workaround for the pci device ordering
in newer 2.6 kernels. This should affect Fedora 10. I can confirm this
"feature not a bug" affects HP DL 3xx servers. Do you remember when we
spoke about this awhile ago on IRC michael? It is very annoying but
can be toggled by setting pci=bfsort or pci=nobfsort in --kopts.

Upstream kernel.org changed the pci device enumeration code which in
turn flipped the default ethernet device names.


>  It looks like they change eth0 to eth1 and then eth1 to eth0, but
> this
>  doesn't seme to make since to me. 

-- 
Jeff Schroeder

Don't drink and derive, alcohol and analysis don't mix.
http://www.digitalprognosis.com

[Michael DeHaan]

Michael DeHaan wrote:
>  I recently made a change so that if a system in Cobbler has multiple
>
>  interfaces but no details about those interfaces, the kickstart is still 
>  valid -- that is to say, it's trivially easy to make a virtual machine 
>  again that has no MAC, IP, or hostname assignments if someone wants.
>
>  However, when I create such a system, I get a network config post 
>  section that I don't /quite/ understand.  As I understand it this code 
>  is intended to reorder the NICs such that they are in the right order 
>  (assumed ok) and optionally set up bonding and vlan information (assumed ok)
>
>  Here's what I get:
>
>  mkdir /etc/sysconfig/network-scripts/cobbler
>  cp /etc/sysconfig/network-scripts/ifcfg-lo 
>  /etc/sysconfig/network-scripts/cobbler/
>  #  Start eth1
>  sed -i "s/eth0/eth1/" /etc/modprobe.conf
>  (
>  grep -v "DEVICE=" /etc/sysconfig/network-scripts/ifcfg-eth0
>  echo "DEVICE=eth1"
>  ) > /etc/sysconfig/network-scripts/cobbler/ifcfg-eth1
>  #  End eth1
>  #  Start eth0
>  sed -i "s/eth1/eth0/" /etc/modprobe.conf
>  (
>  grep -v "DEVICE=" /etc/sysconfig/network-scripts/ifcfg-eth1
>  echo "DEVICE=eth0"
>  ) > /etc/sysconfig/network-scripts/cobbler/ifcfg-eth0
>  #  End eth0
>  rm -f /etc/sysconfig/network-scripts/ifcfg-*
>  mv /etc/sysconfig/network-scripts/cobbler/* /etc/sysconfig/network-scripts/
>  rm -r /etc/sysconfig/network-scripts/cobbler
>  cat /etc/modprobe.conf.cobbler >> /etc/modprobe.conf
>  rm -f /etc/modprobe.conf.cobbler
>  # End post_install_network_config generated code
>
>
>   From the above, the two sed lines look redundant.   What are they 
>  intended to do?
>
>  It looks like they change eth0 to eth1 and then eth1 to eth0, but this 
>  doesn't seme to make since to me.
>
>  --Michael
>
>
>
>
>
>
>  _______________________________________________
>  cobbler mailing list
>  cobbler(a)lists.fedorahosted.org
>  https://fedorahosted.org/mailman/listinfo/cobbler
>     
To elaborate, this swaps eth0 for eth1, so if there was a eth0 and an 
eth1 in the file, it finishes up with both of them being called eth1, 
which seems wrong to me.

The code in question is the post_network_config_snippet.

I've gone through (despite my earlier recommendations against it) and 
indented everything ... it will produce weirdly formatted output in the 
ks now but is easier to read, so if folks want to give reading that and 
debugging it a crack, that would be useful.

Meanwhile I'll do some more extended testing with various combinations 
to see that the templates continue to function.  The bonding/vlan stuff 
may be labelled "experimental" for a while though we obviously want to 
make sure the simple cases (eth0, eth1) etc work -- static or not 
static, partial information supplied or lots, etc.

--Michael

[Jasper Capel]

Michael DeHaan wrote:
>   From the above, the two sed lines look redundant.   What are they 
>  intended to do?
>  
>  It looks like they change eth0 to eth1 and then eth1 to eth0, but this 
>  doesn't seme to make since to me.
>  
>  --Michael
>   
The code should be changed so it doesn't do any NIC reordering when not 
all interfaces have MAC addresses specified on them. I think we should 
just assume the user provided interface names are as-they-are on the 
system, and don't support interface renaming unless MAC-addresses are 
specified.

Jasper

[Jasper Capel]

Jasper Capel wrote:
>  Michael DeHaan wrote:
> >  From the above, the two sed lines look redundant.   What are they 
> > intended to do?
> >
> > It looks like they change eth0 to eth1 and then eth1 to eth0, but this 
> > doesn't seme to make since to me.
> >
> > --Michael
> >
>  
>  The code should be changed so it doesn't do any NIC reordering when not 
>  all interfaces have MAC addresses specified on them. I think we should 
>  just assume the user provided interface names are as-they-are on the 
>  system, and don't support interface renaming unless MAC-addresses are 
>  specified.
>  
>  Jasper
>   
Fix pushed to my networking branch, for scenarios where not all 
MAC-addresses are specified in Cobbler. If Cobbler does have 
MAC-addresses for /all/ physical interfaces, it will honor whatever name 
the user gives those interfaces, so eth0->foo, eth1->bar, eth2->eth0 
would be possible.

Jasper