On 12/05/2012 04:14 AM, Osier Yang wrote:
On 2012年12月05日 19:03, Jiri Denemark wrote:
On Wed, Dec 05, 2012 at 18:54:42 +0800, Osier Yang wrote: ...
However, the mainly reason I choosed to use a sub-list of domain names is for future extenstion, I.E. Assuming there are other disk setting (you never known how many they will be), we have to guarantee they are same among guests in future. Looking up the disk def with domain and disk path gives us much flexibility IMHO.
So the point of the argument is: the trade between the flexibility and the uncomfortable locks.
OK, I guess we can store more info in the sharedDisks list (either today or later when we need it), we may even store the domain list there, but we don't definitely want to go through all the domains to get the required details.
I think it should be just a few guests share the disk in practice, which means in practice the sharedDisks->disks[i]->ndomains should be short. And that's the other reason why I can live with the locks. Though in theory, it can be all domains (assuming it's large number) share the disk.
The other question is: Aren't we already go through all domain objects in many places?
I'm stepping in a bit late, and haven't fully looked at the series yet, but one of the things that I would love for libvirt to someday have is a way to get a list of all virStorageVolPtr associated with any given virDomainPtr, and conversely, given a virStorageVolPtr, return a list of all virDomainPtr that use the file (whether directly, or whether as a backing file). To get to that point, I envision having a way for every <disk> element to be tied to a virStorageVolPtr, even if it means the implicit creation of a transient virStoragePoolPtr directory-based pool for any <disk> specified without an explicit pool. Then, creation of a new domain, as well as hot-plugging of any disks to an existing domain, will update each affected virStorageVolPtr; and you really _should_ be maintaining a list of all associated domains with the disk object. Thus, I think searching whether a shared disk is allowed should be a matter of asking that shared disk what domains it is already associated with, rather than asking each domain whether it uses the shared disk. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org