Xen devel - Jun 2010 - [PATCH] xend: Do not mess with bridge if admin has set one up already

Previously, the default "network-script",
/etc/xen/scripts/network-bridge, would attempt to do its horrid work
even if you had already set everything up in /etc/network/interfaces.

Setting up your bridge in /etc/network/interfaces is:
 * easy
 * required for libxl since libxl never does it for you
 * not a fragile piece of lunacy
 * properly documented
 * the way everyone would expect it to work

In this small patch we make it so that the default config for xend
doesn''t mess about on startup if you already have a bridge, and
doesn''t mess about on shutdown unless your first-named bridge (eth0 or
xenbr0, normally) doesn''t also have a physical interface named
p<whatever> (peth0 or pxenbr0) enslaved to it.  The latter test is not
ideal but will hopefully do from now until the time xend finally dies.

We also fix the "documentation" - ie, the comments in the default
xend-config.sxp - to correspond to reality.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>


diff -r 125b3493dac9 tools/examples/xend-config.sxp
--- a/tools/examples/xend-config.sxp	Fri Jun 11 11:37:22 2010 +0100
+++ b/tools/examples/xend-config.sxp	Mon Jun 14 16:07:02 2010 +0100
@@ -147,8 +147,22 @@
 #
 # (network-script ''network-bridge netdev=eth1'')
 #
-# The bridge is named xenbr0, by default.  To rename the bridge, use
+# The bridge is named eth0, by default (yes, really!)
 #
+
+# It is normally much better to create the bridge yourself in
+# /etc/network/interfaces.  network-bridge start does nothing if you
+# already have a bridge, and network-bridge stop does nothing if the
+# default bridge name (normally eth0) is not a bridge.  See
+# bridge-utils-interfaces(5) for full information on the syntax in
+# /etc/network/interfaces, but you probably want something like this:
+#    iface xenbr0 inet static
+#        address [etc]
+#        netmask [etc]
+#        [etc]
+#        bridge_ports eth0
+#
+# To have network-bridge create a differently-named bridge, use:
 # (network-script ''network-bridge bridge=<name>'')
 #
 # It is possible to use the network-bridge script in more complicated
@@ -169,7 +183,8 @@
 # configuring a new vif, but a value specified here would act as a default.
 #
 # If you are using only one bridge, the vif-bridge script will discover that,
-# so there is no need to specify it explicitly.
+# so there is no need to specify it explicitly.  The default is to use
+# the bridge which is listed first in the output from brctl.
 #
 (vif-script vif-bridge)
 
diff -r 125b3493dac9 tools/hotplug/Linux/network-bridge
--- a/tools/hotplug/Linux/network-bridge	Fri Jun 11 11:37:22 2010 +0100
+++ b/tools/hotplug/Linux/network-bridge	Mon Jun 14 16:07:02 2010 +0100
@@ -216,6 +216,10 @@
 	return
     fi
 
+    if [ `brctl show | wc -l` != 1 ]; then
+        return
+    fi
+
     if link_exists "$pdev"; then
         # The device is already up.
         return
@@ -263,6 +267,10 @@
     fi
     if ! link_exists "$bridge"; then
 	return
+    fi
+    if ! [ -e "/sys/class/net/${bridge}/brif/${pdev}" ]; then
+        # $bridge is not a bridge to which pdev is enslaved
+        return
     fi
 
     claim_lock "network-bridge"

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On Mon, Jun 14, 2010 at 04:07:07PM +0100, Ian Jackson
wrote:
> Previously, the default "network-script",
> /etc/xen/scripts/network-bridge, would attempt to do its horrid work
> even if you had already set everything up in /etc/network/interfaces.
> 
Instead of talking about "/etc/network/interfaces" you could write 
"distro-specific network scripts like /etc/network/interfaces or
/etc/sysconfig/network-scripts/ifcfg-*" :)

-- Pasi
> Setting up your bridge in /etc/network/interfaces is:
>  * easy
>  * required for libxl since libxl never does it for you
>  * not a fragile piece of lunacy
>  * properly documented
>  * the way everyone would expect it to work
> 
> In this small patch we make it so that the default config for xend
> doesn''t mess about on startup if you already have a bridge, and
> doesn''t mess about on shutdown unless your first-named bridge
(eth0 or
> xenbr0, normally) doesn''t also have a physical interface named
> p<whatever> (peth0 or pxenbr0) enslaved to it.  The latter test is
not
> ideal but will hopefully do from now until the time xend finally dies.
> 
> We also fix the "documentation" - ie, the comments in the default
> xend-config.sxp - to correspond to reality.
> 
> Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
> 
> 
> diff -r 125b3493dac9 tools/examples/xend-config.sxp
> --- a/tools/examples/xend-config.sxp	Fri Jun 11 11:37:22 2010 +0100
> +++ b/tools/examples/xend-config.sxp	Mon Jun 14 16:07:02 2010 +0100
> @@ -147,8 +147,22 @@
>  #
>  # (network-script ''network-bridge netdev=eth1'')
>  #
> -# The bridge is named xenbr0, by default.  To rename the bridge, use
> +# The bridge is named eth0, by default (yes, really!)
>  #
> +
> +# It is normally much better to create the bridge yourself in
> +# /etc/network/interfaces.  network-bridge start does nothing if you
> +# already have a bridge, and network-bridge stop does nothing if the
> +# default bridge name (normally eth0) is not a bridge.  See
> +# bridge-utils-interfaces(5) for full information on the syntax in
> +# /etc/network/interfaces, but you probably want something like this:
> +#    iface xenbr0 inet static
> +#        address [etc]
> +#        netmask [etc]
> +#        [etc]
> +#        bridge_ports eth0
> +#
> +# To have network-bridge create a differently-named bridge, use:
>  # (network-script ''network-bridge bridge=<name>'')
>  #
>  # It is possible to use the network-bridge script in more complicated
> @@ -169,7 +183,8 @@
>  # configuring a new vif, but a value specified here would act as a
default.
>  #
>  # If you are using only one bridge, the vif-bridge script will discover
that,
> -# so there is no need to specify it explicitly.
> +# so there is no need to specify it explicitly.  The default is to use
> +# the bridge which is listed first in the output from brctl.
>  #
>  (vif-script vif-bridge)
>  
> diff -r 125b3493dac9 tools/hotplug/Linux/network-bridge
> --- a/tools/hotplug/Linux/network-bridge	Fri Jun 11 11:37:22 2010 +0100
> +++ b/tools/hotplug/Linux/network-bridge	Mon Jun 14 16:07:02 2010 +0100
> @@ -216,6 +216,10 @@
>  	return
>      fi
>  
> +    if [ `brctl show | wc -l` != 1 ]; then
> +        return
> +    fi
> +
>      if link_exists "$pdev"; then
>          # The device is already up.
>          return
> @@ -263,6 +267,10 @@
>      fi
>      if ! link_exists "$bridge"; then
>  	return
> +    fi
> +    if ! [ -e "/sys/class/net/${bridge}/brif/${pdev}" ]; then
> +        # $bridge is not a bridge to which pdev is enslaved
> +        return
>      fi
>  
>      claim_lock "network-bridge"
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
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Pasi Kärkkäinen writes ("Re: [Xen-devel] [PATCH] xend: Do not mess with
bridge if admin has set one up already"):
> On Mon, Jun 14, 2010 at 04:07:07PM +0100, Ian Jackson wrote:
> > Previously, the default "network-script",
> > /etc/xen/scripts/network-bridge, would attempt to do its horrid work
> > even if you had already set everything up in /etc/network/interfaces.
> 
> Instead of talking about "/etc/network/interfaces" you could
write
> "distro-specific network scripts like /etc/network/interfaces or
/etc/sysconfig/network-scripts/ifcfg-*" :)
I look forward to your patch on top of mine :-).

Ian.

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>-----Original Message-----
>From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-
>bounces@lists.xensource.com] On Behalf Of Ian Jackson
>Sent: Monday, June 14, 2010 8:07 AM
>To: xen-devel@lists.xensource.com
>Subject: [Xen-devel] [PATCH] xend: Do not mess with bridge if admin has
>set one up already
>
>Previously, the default "network-script",
>/etc/xen/scripts/network-bridge, would attempt to do its horrid work
>even if you had already set everything up in /etc/network/interfaces.
>
>Setting up your bridge in /etc/network/interfaces is:
> * easy
> * required for libxl since libxl never does it for you
> * not a fragile piece of lunacy
> * properly documented
> * the way everyone would expect it to work
>
>In this small patch we make it so that the default config for xend
>doesn''t mess about on startup if you already have a bridge, and
>doesn''t mess about on shutdown unless your first-named bridge (eth0
or
>xenbr0, normally) doesn''t also have a physical interface named
>p<whatever> (peth0 or pxenbr0) enslaved to it.  The latter test is not
>ideal but will hopefully do from now until the time xend finally dies.
>
>We also fix the "documentation" - ie, the comments in the default
>xend-config.sxp - to correspond to reality.
>
>Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Finally!  Much Appreciated!!!

For too long I''ve had to hack the scripts every time I install a new
Xen setup so that it won''t muck with my custom bridge settings.

Thanks!!!!

- Greg


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On Mon, 2010-06-14 at 16:07 +0100, Ian Jackson wrote:
> Previously, the default "network-script",
> /etc/xen/scripts/network-bridge, would attempt to do its horrid work
> even if you had already set everything up in /etc/network/interfaces.
I like it. One of the first patches I apply to any newly cloned Xen tree
is:

diff -r 2d74cb5f973f -r ed212583c51b tools/examples/xend-config.sxp
--- a/tools/examples/xend-config.sxp	Thu Jun 10 10:19:26 2010 +0100
+++ b/tools/examples/xend-config.sxp	Fri Jun 11 11:01:02 2010 +0100
@@ -154,7 +154,7 @@
 # two fake interfaces per guest domain.  To do things like this, write
 # yourself a wrapper script, and call network-bridge from it, as appropriate.
 #
-(network-script network-bridge)
+#(network-script network-bridge)
 
 # The script used to control virtual interfaces.  This can be overridden on a
 # per-vif basis when creating a domain or a configuring a new vif.  The

Which is slightly more aggressive.
> Setting up your bridge in /etc/network/interfaces is:
>  * easy
FWIW I typically use a stanza like:
        iface xenbr0 inet dhcp
                bridge_ports eth0
                bridge_stp off
                bridge_waitport 0
                bridge_fd 0
                bridge_maxwait 0
        
I think only bridge_ports is strictly required but the others are
useful. As you note in the patch the bridge-utils-interfaces(5) manpage
describes the available settings.

Ian.


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On 16/06/2010 09:23, "Ian Campbell" <Ian.Campbell@citrix.com>
wrote:
> On Mon, 2010-06-14 at 16:07 +0100, Ian Jackson wrote:
>> Previously, the default "network-script",
>> /etc/xen/scripts/network-bridge, would attempt to do its horrid work
>> even if you had already set everything up in /etc/network/interfaces.
> 
> I like it. One of the first patches I apply to any newly cloned Xen tree
> is:
I wonder should we supply any init/hotplug/udev scripts at all?

 -- Keir
> diff -r 2d74cb5f973f -r ed212583c51b tools/examples/xend-config.sxp
> --- a/tools/examples/xend-config.sxp Thu Jun 10 10:19:26 2010 +0100
> +++ b/tools/examples/xend-config.sxp Fri Jun 11 11:01:02 2010 +0100
> @@ -154,7 +154,7 @@
>  # two fake interfaces per guest domain.  To do things like this, write
>  # yourself a wrapper script, and call network-bridge from it, as
appropriate.
>  #
> -(network-script network-bridge)
> +#(network-script network-bridge)
>  
>  # The script used to control virtual interfaces.  This can be overridden
on a
>  # per-vif basis when creating a domain or a configuring a new vif.  The
> 
> Which is slightly more aggressive.
> 
>> Setting up your bridge in /etc/network/interfaces is:
>>  * easy
> 
> FWIW I typically use a stanza like:
>         iface xenbr0 inet dhcp
>                 bridge_ports eth0
>                 bridge_stp off
>                 bridge_waitport 0
>                 bridge_fd 0
>                 bridge_maxwait 0
>         
> I think only bridge_ports is strictly required but the others are
> useful. As you note in the patch the bridge-utils-interfaces(5) manpage
> describes the available settings.
> 
> Ian.
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel


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Keir Fraser writes ("Re: [Xen-devel] [PATCH] xend: Do not mess with bridge
if admin has set one up already"):
> I wonder should we supply any init/hotplug/udev scripts at all?
We do still need to supply hotplug scripts to plumb block and vif
backends to the appropriate dom0 resources.  When you''re using xl,
that''s all you need.

Ian.

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On Wed, 2010-06-16 at 09:39 +0100, Keir Fraser wrote:
> On 16/06/2010 09:23, "Ian Campbell"
<Ian.Campbell@citrix.com> wrote:
> 
> > On Mon, 2010-06-14 at 16:07 +0100, Ian Jackson wrote:
> >> Previously, the default "network-script",
> >> /etc/xen/scripts/network-bridge, would attempt to do its horrid
work
> >> even if you had already set everything up in
/etc/network/interfaces.
> > 
> > I like it. One of the first patches I apply to any newly cloned Xen
tree
> > is:
> 
> I wonder should we supply any init/hotplug/udev scripts at all?
Including something in tools/examples (where they already live today)
seems reasonable to provide, well, examples.

I''m not sure it always makes sense to install all of them, at least by
default. But perhaps that is a case by case determination (initscripts
are different beasts to udev configuration etc)?




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