Xen devel - Feb 2006 - [PATCH] don''t require ebtables in the host kernel

The network-bridge script fails when setting a few sysctls
which are only available if ebtables is present in the host
kernel. Fix by ignoring the return value of the sysctl command.

Signed-off-by: Avi Kivity <avi@qumranet.com>

Index: xen/tools/examples/network-bridge
==================================================================---
xen/tools/examples/network-bridge	(revision 991)
+++ xen/tools/examples/network-bridge	(revision 992)
@@ -158,9 +158,9 @@
 
     # Don''t create the bridge if it already exists.
     if ! brctl show | grep -q ${bridge} ; then
-	sysctl -w "net.bridge.bridge-nf-call-arptables=0"
-	sysctl -w "net.bridge.bridge-nf-call-ip6tables=0"
-	sysctl -w "net.bridge.bridge-nf-call-iptables=0"
+	! sysctl -w "net.bridge.bridge-nf-call-arptables=0"
+	! sysctl -w "net.bridge.bridge-nf-call-ip6tables=0"
+	! sysctl -w "net.bridge.bridge-nf-call-iptables=0"
 	brctl addbr ${bridge}
 	brctl stp ${bridge} off
 	brctl setfd ${bridge} 0


-- 
error compiling committee.c: too many arguments to function


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On Wed, Feb 22, 2006 at 10:54:51AM +0200, Avi Kivity wrote:
> The network-bridge script fails when setting a few sysctls
> which are only available if ebtables is present in the host
> kernel. Fix by ignoring the return value of the sysctl command.
> 
> Signed-off-by: Avi Kivity <avi@qumranet.com>
> 
> Index: xen/tools/examples/network-bridge
> ==================================================================> ---
xen/tools/examples/network-bridge	(revision 991)
> +++ xen/tools/examples/network-bridge	(revision 992)
> @@ -158,9 +158,9 @@
> 
>     # Don''t create the bridge if it already exists.
>     if ! brctl show | grep -q ${bridge} ; then
> -	sysctl -w "net.bridge.bridge-nf-call-arptables=0"
> -	sysctl -w "net.bridge.bridge-nf-call-ip6tables=0"
> -	sysctl -w "net.bridge.bridge-nf-call-iptables=0"
> +	! sysctl -w "net.bridge.bridge-nf-call-arptables=0"
> +	! sysctl -w "net.bridge.bridge-nf-call-ip6tables=0"
> +	! sysctl -w "net.bridge.bridge-nf-call-iptables=0"
> 	brctl addbr ${bridge}
> 	brctl stp ${bridge} off
> 	brctl setfd ${bridge} 0
Where did this network-bridge script come from?  The stock Xen-3.0
network-bridge doesn''t have these sysctl lines in the first place.

Furthermore, using ! doesn''t ignore the return value -- it inverts it. 
I''d be
surprised if this works in systems that _do_ have ebtables.

Ewan.

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Ewan Mellor wrote:
>>--- xen/tools/examples/network-bridge	(revision 991)
>>+++ xen/tools/examples/network-bridge	(revision 992)
>>@@ -158,9 +158,9 @@
>>
>>    # Don''t create the bridge if it already exists.
>>    if ! brctl show | grep -q ${bridge} ; then
>>-	sysctl -w "net.bridge.bridge-nf-call-arptables=0"
>>-	sysctl -w "net.bridge.bridge-nf-call-ip6tables=0"
>>-	sysctl -w "net.bridge.bridge-nf-call-iptables=0"
>>+	! sysctl -w "net.bridge.bridge-nf-call-arptables=0"
>>+	! sysctl -w "net.bridge.bridge-nf-call-ip6tables=0"
>>+	! sysctl -w "net.bridge.bridge-nf-call-iptables=0"
>>	brctl addbr ${bridge}
>>	brctl stp ${bridge} off
>>	brctl setfd ${bridge} 0
>>    
>>
>
>Where did this network-bridge script come from?  The stock Xen-3.0
>network-bridge doesn''t have these sysctl lines in the first place.
>  
>
It comes from FC5. Sorry, should have checked the pristine Xen sources. 
Sorry about the noise.
>Furthermore, using ! doesn''t ignore the return value -- it inverts
it.  I''d be
>surprised if this works in systems that _do_ have ebtables.
>  
>
No, ! on the beginning of a command tells bash to ignore the exit code:

    `-e''
          Exit immediately if a simple command (*note Simple
          Commands::) exits with a non-zero status, unless the command
          that fails is part of the command list immediately following
          a `while'' or `until'' keyword, part of the test in an
`if''
          statement, part of a `&&'' or `||'' list, or
if the command''s
          return status is being inverted using `!''.  A trap on
`ERR'',
          if set, is executed before the shell exits.

''sysctl -ew'' would have been better though.

-- 
error compiling committee.c: too many arguments to function


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