[libvirt] Quorum block driver libvirt support proposal

[Eric Blake]

On 05/16/2014 04:33 AM, Benoît Canet wrote:
>                                                                                 
> I want to make use of the new backingStore xml element to implement quorum.     
>                                                                                 
> Proposed Quorum libvirt format:                                                 
> -------------------------------                                                 
>                                                                                 
> <disk type='quorum' device='disk'>                                              
>   <driver name='qemu' type='quorum'/>                                           
>   <threshold value=2/>                                                          

Rather than making <threshold> a sub-element, I'd stick it as an
attribute, as in:

<disk type='quorum' threshold='2' device='disk'>

>                                                                                 
> * Add VIR_STORAGE_TYPE_QUORUM                                                     
>                                                                                 
> * In src/util/virstoragefile.h change _virStorageSource to contain a              
> virStorageSourcePtrPtr backingStores.                                           

PtrPtr doesn't make sense.  Just keep it as a single pointer, but add an
nBackingStores field and treat it as an array (all existing callers are
now an array of 1, quorum is a new array of N).

> I think doing it at this level allow to keep a 1-1 mapping with the qemu        
> BlockDriverState hiearchy                                                       
>                                                                                 
> * Add a int quorum_threshold field to the same structure                          

size_t, not int

>                                                                                 
> * Add support for parsing treshold in virDomainDiskDefParseXML                    
>                                                                                 
> * Change virDomainDiskBackingStoreParse to virDomainDiskBackingStoresParse to parse
> all the backingStore at once an use realloc to grow the backingStores field.    
>                                                                                 
> * Modify virDomainDiskDefFormat to call virDomainDiskBackingStoreFormat in a loop
>   for saving
>                                                                                 
> * hook into qemuBuildDriveStr around line 3442 to create the quorum parameters    
> 
> Do you feel that I am missing something ?

We'll probably find more as you go, but this sounds like a reasonable start


-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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