Xen devel - Dec 2005 - overwriting config files on re-install, and vif''s

Every time I install xen, it clobbers my /etc/xend-config.sxp config
file, which I think is a bit rude :)

Would it hurt to detect if the file exists already, and if it does
already, create a /etc/xend-config.sxp.new instead?

Also, I now seem to have the following interfaces hanging around, even
before I create any domains:

2: vif0.0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
3: veth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
4: vif0.1: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
5: veth1: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
6: vif0.2: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
7: veth2: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
8: vif0.3: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
9: veth3: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
10: vif0.4: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
11: veth4: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
12: vif0.5: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
13: veth5: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
14: vif0.6: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
15: veth6: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
16: vif0.7: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
17: veth7: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
    link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff

Are they really necessary? Are they cruft from xen remembering vif''s
created from time gone by, or created automatically?

Thanks

James

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On Wednesday 21 December 2005 04:50, James Harper wrote:
> 17: veth7: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
>     link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
>
> Are they really necessary? Are they cruft from xen remembering
vif''s
> created from time gone by, or created automatically?
>
It is automatically created (netback/loopback.c). 

I do not understand well why we need to previously create all this, and not 
use an "as needed" approach.

-- 
Murillo Fernandes Bernardes
IBM Linux Technology Center

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On Wed, Dec 21, 2005 at 05:50:42PM +1100, James Harper wrote:
> Also, I now seem to have the following interfaces hanging around, even
> before I create any domains:
> 
> 2: vif0.0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
>     link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
> 3: veth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
>     link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
>
> [etc]
> 
> Are they really necessary? Are they cruft from xen remembering
vif''s
> created from time gone by, or created automatically?
They are the 8 netback-loopback interface pairs.  These are used to connect
dom0''s virtual ethernet through a bridge (or whatever) and then out
through
the physical ethernet interface.  8 interfaces allows you 8 physical NICs.  If
you want to reduce this number, it''s the parameter nloopbacks to our
loopback
module (see drivers/xen/netback/loopback.c.  They aren''t doing any harm
though,
so I''d not worry about it.

Ewan.

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> 
> They are the 8 netback-loopback interface pairs.  These are used to
> connect
> dom0''s virtual ethernet through a bridge (or whatever) and then
out
> through
> the physical ethernet interface.  8 interfaces allows you 8 physical
NICs.
> If
> you want to reduce this number, it''s the parameter nloopbacks to
our
> loopback
> module (see drivers/xen/netback/loopback.c.  They aren''t doing any
harm
> though,
> so I''d not worry about it.
I''ve had a look through loopback.c and can see the code that creates
them, and the parameter that says how many to create.

Seems a bit of a waste of resources, but the thing I find annoying
though is it turns the output of ''ip link'' from a few lines to
a page.
But I''ll live with it :)

Thanks for clearing it up.

James

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> Every time I install xen, it clobbers my /etc/xend-config.sxp 
> config file, which I think is a bit rude :)
> 
> Would it hurt to detect if the file exists already, and if it 
> does already, create a /etc/xend-config.sxp.new instead?
Yep, this would definitely be preferred. I suspect most people use the
RPMs, so which shouldn''t have these problems.

We could certainly do with an install.sh script that was smarter (and
did uninstall).

Ian

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