[Xen-devel] Re: Rename all dying domains to be prefixed with Zombie. This allows a new domain

[Sean Dague <sean@xxxxxxxxx>]

So what happens if:

* Dom1 is told to die
* It doesn't because it can't free a physical resource (i.e. disk)
* It gets renamed to Zombie-Dom1
* User tries to recreate Dom1
* New Dom1 grabs physical resource that was keeping Dom1 from dying

Doesn't that provide for the possibility of 2 writers to a device that only
can support 1, and all heck breaking loose?  (Note, I hope I'm wrong here)

It seems that this just moves the race to somewhere more dangerous.

        -Sean

On Thu, Oct 06, 2005 at 10:16:12AM +0000, Xen patchbot -unstable wrote:
> Diffstat output:
> 
>  XendDomainInfo.py |   33 ++++++++++++++++++++++-----------
>  1 files changed, 22 insertions(+), 11 deletions(-)
> 
> # HG changeset patch
> # User emellor@ewan
> # Node ID 0bc466c255605d0efeb4803626b72415839b9e6c
> # Parent  1cfe0875658d5f83d38a5d96abe7a66e0d5db508
> Rename all dying domains to be prefixed with Zombie.  This allows a new domain
> to be created with the same name, fixing the race condition inside XendDomain
> that caused bug #278.
> 
> Move the state_set(TERMINATED) call onto the end of cleanupDomain rather than
> destroyDomain, so that this flag is set when XendDomain cleans up a domain
> that was killed without going through Xend.
> 
> Remove is_terminated, as this check is no longer necessary, since we are using
> Zombie prefixes instead.
> 
> Signed-off-by: Ewan Mellor <ewan@xxxxxxxxxxxxx>
> 
> diff -r 1cfe0875658d -r 0bc466c25560 tools/python/xen/xend/XendDomainInfo.py
> --- a/tools/python/xen/xend/XendDomainInfo.py Thu Oct  6 10:04:49 2005
> +++ b/tools/python/xen/xend/XendDomainInfo.py Thu Oct  6 10:09:14 2005
> @@ -97,6 +97,7 @@
>  DOMROOT = '/local/domain/'
>  VMROOT  = '/vm/'
>  
> +ZOMBIE_PREFIX = 'Zombie-'
>  
>  xc = xen.lowlevel.xc.new()
>  xroot = XendRoot.instance()
> @@ -997,8 +998,6 @@
>          dominfo = domain_by_name(name)
>          if not dominfo:
>              return
> -        if dominfo.is_terminated():
> -            return
>          if self.domid is None:
>              raise VmError("VM name '%s' already in use by domain %d" %
>                            (name, dominfo.domid))
> @@ -1100,6 +1099,14 @@
>          except:
>              log.exception("Removing domain path failed.")
>  
> +        try:
> +            if not self.info['name'].startswith(ZOMBIE_PREFIX):
> +                self.info['name'] = self.generateZombieName()
> +        except:
> +            log.exception("Renaming Zombie failed.")
> +
> +        self.state_set(STATE_VM_TERMINATED)
> +
>  
>      def cleanupVm(self):
>          """Cleanup VM resources.  Idempotent.  Nothrow guarantee."""
> @@ -1123,23 +1130,15 @@
>          log.debug("XendDomainInfo.destroyDomain(%s)", str(self.domid))
>  
>          self.cleanupDomain()
> -        
> +
>          try:
>              if self.domid is not None:
>                  xc.domain_destroy(dom=self.domid)
>          except:
>              log.exception("XendDomainInfo.destroy: xc.domain_destroy 
> failed.")
>  
> -        self.state_set(STATE_VM_TERMINATED)
> -
>  
>      ## private:
> -
> -    def is_terminated(self):
> -        """Check if a domain has been terminated.
> -        """
> -        return self.state == STATE_VM_TERMINATED
> -
>  
>      def release_devices(self):
>          """Release all domain's devices.  Nothrow guarantee."""
> @@ -1353,6 +1352,18 @@
>                  n += 1
>  
>  
> +    def generateZombieName(self):
> +        n = 0
> +        name = ZOMBIE_PREFIX + self.info['name']
> +        while True:
> +            try:
> +                self.check_name(name)
> +                return name
> +            except VmError:
> +                n += 1
> +                name = "%s%d-%s" % (ZOMBIE_PREFIX, n, self.info['name'])
> +
> +
>      def configure_bootloader(self):
>          if not self.info['bootloader']:
>              return
> 
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> 

-- 
__________________________________________________________________

Sean Dague                                       Mid-Hudson Valley
sean at dague dot net                            Linux Users Group
http://dague.net                                 http://mhvlug.org

There is no silver bullet.  Plus, werewolves make better neighbors
than zombies, and they tend to keep the vampire population down.
__________________________________________________________________

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