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[Cluster-devel] Re: [Libvir] virDomainDump() API (equivalent to xm dump) in libvirt?



On Fri, Nov 03, 2006 at 10:38:18AM -0500, Lon Hohberger wrote:
> There's already one for saving live domains:
> 
> int virDomainSave(virDomainPtr domain, const char *to);
> 
> Why not use a similar API for a function which does the equivalent of
> 'xm dump' ?

  I assume you mean 'xm dump-core' actually 

> int virDomainDump(virDomainPtr domain, const char *to, int flags);
> 
> Create a kernel dump of the domain in the path contained in *to.  This
> API must fail if the domain is not in a panicked/crashed state.
> If you set the lowest-bit in flags, however, you can override this
> behavior: if the lowest bit is set, the domain will first be crashed
> (similar to SysRq-C) - then a dump will be taken from that.
> 
> 
> Why?
> 
> In the event that a cluster node needs to fence a Xen domain (or other
> management tools, to be sure), we could use the API to generate a core
> of the domain (if it panicked) to help debug the problem prior to
> restarting the domain.
> 
> The 'crash-before-dump' bit is just something someone might want to use
> at some point; I don't think it is absolutely necessary - but it doesn't
> hurt anything either.

  Okay I can see how this would be useful, the questions I would have would be:
    - how generic is this, i.e. suppose a different hypervisor back-end
      would this still make sense. I guess yes, for example with an UML
      back-end we could check the process status and force a dump with a
      signal and move the core to the given file not trivial but same semantic
      would be doable.
    - can we implement it with current xen, again yes, we should be able
      if we have a full connection (root) to do the same as 'xm dump-core'
    - is the API clean enough, I guess the semantic is relatively clear
      instead of stating 'If you set the lowest-bit in flags' I would rather
      define a DumpFlags enum and state that flags is an or'ing of any of them
      I would probably name the function virDomainDumpCore though to not
      confuse with virDomainSave 

 So yes, why not, you want to work on it ? Or should I (or any candidate).

Daniel

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Daniel Veillard      | virtualization library  http://libvirt.org/
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