[libvirt] [PATCH] use -w flag if supported by iptables

[Daniel P. Berrange]

On Fri, Nov 01, 2013 at 09:17:58AM -0500, Serge Hallyn wrote:
> Quoting Daniel P. Berrange (berrange at redhat.com):
> > On Thu, Oct 31, 2013 at 04:36:24PM -0500, Serge Hallyn wrote:
> > > This will properly lock libvirt's usage of iptables with
> > > others (like ufw).
> > > 
> > > (See https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1245322)
> > > 
> > > Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
> > > ---
> > >  src/util/viriptables.c | 30 ++++++++++++++++++++++++++----
> > >  1 file changed, 26 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/src/util/viriptables.c b/src/util/viriptables.c
> > > index 16f571e..30d59b6 100644
> > > --- a/src/util/viriptables.c
> > > +++ b/src/util/viriptables.c
> > > @@ -50,19 +50,25 @@
> > >  #include "virstring.h"
> > >  #include "virutil.h"
> > >  
> > > +bool iptables_supports_xlock = false;
> > > +
> > >  #if HAVE_FIREWALLD
> > >  static char *firewall_cmd_path = NULL;
> > > +#endif
> > >  
> > >  static int
> > >  virIpTablesOnceInit(void)
> > >  {
> > > +    virCommandPtr cmd;
> > > +    int status;
> > > +
> > > +#if HAVE_FIREWALLD
> > >      firewall_cmd_path = virFindFileInPath("firewall-cmd");
> > >      if (!firewall_cmd_path) {
> > >          VIR_INFO("firewall-cmd not found on system. "
> > >                   "firewalld support disabled for iptables.");
> > >      } else {
> > > -        virCommandPtr cmd = virCommandNew(firewall_cmd_path);
> > > -        int status;
> > > +        virCommandNew(firewall_cmd_path);
> > >  
> > >          virCommandAddArgList(cmd, "--state", NULL);
> > >          if (virCommandRun(cmd, &status) < 0 || status != 0) {
> > > @@ -74,13 +80,26 @@ virIpTablesOnceInit(void)
> > >          }
> > >          virCommandFree(cmd);
> > >      }
> > > +
> > > +    if (firewall_cmd_path)
> > > +        return 0;
> > > +
> > > +#endif
> > > +
> > > +    cmd = virCommandNew(IPTABLES_PATH);
> > > +    virCommandAddArgList(cmd, "-w", "-L", "-n", NULL);
> > 
> > What version of iptables actually has this '-w' flag ? The ubuntu bug
> 
> It was introduced in 1.4.20, specifically with 
> 
> commit 93587a04d0f2511e108bbc4d87a8b9d28a5c5dd8
> Author: Phil Oester <kernel at linuxace.com>
> Date:   Fri May 31 09:07:04 2013 -0400
> 
>     ip[6]tables: Add locking to prevent concurrent instances
> 
> > points to an upstream patch, which does locking unconditionally, no
> > mention of any '-w' flag.
> 
> Well yes it locks unconditionally, but without -w it won't wait.  So
> if there is another app using iptables at the time, then the call fails
> and libvirt fails to create the interface.
> 
> > Looking on a per-rule basis is pretty lame locking, since changes
> > to iptables are often comprised of many rule changes :-(
> > 
> > > +    if (virCommandRun(cmd, &status) < 0 || status != 0) {
> > > +        VIR_INFO("xtables locking not supported by your iptables");
> > > +    } else {
> > > +        VIR_INFO("using xtables locking for iptables");
> > > +        iptables_supports_xlock = true;
> > > +    }
> > > +    virCommandFree(cmd);
> > >      return 0;
> > >  }
> > >  
> > >  VIR_ONCE_GLOBAL_INIT(virIpTables)
> > >  
> > > -#endif
> > > -
> > 
> > The call to virIptablesInitialize is protected by
> > #if HAVE_FIREWALLD too, so this code will not run
> > on older distros.
> 
> I thought I changed that, but I may not properly understand the
> libvirt init code.  I moved the VIR_ONCE_GLOBAL_INIT(virIptTables)
> out from under that ifdef.

That macro just does the declaration of the initializer - this still
needs to be actually invoked - which is what the (conditional) calls
to virIptablesInitialize() later in the file do.

Daniel
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