Re: [libvirt] [PATCH] Increased upper limit on lists of pool names

On 03/15/2012 05:51 AM, Daniel P. Berrange wrote: > On Thu, Mar 15, 2012 at 06:22:38AM -0500, Jesse Cook wrote: >> Just to clarify, you would like to see: I have not actually tried this, but based on my understanding of the RPC famework, I'd expect: >> >> v0.9.10 pre-patch client talk to v0.9.10 patch server If there are 256 or fewer names, this works as it always did. If there are more than 256 names, then the server tries to send back more array elements than the client is prepared to receive - the client will treat the response as an invalid RPC, and my recollection is that under these circumstances, the client then forcefully disconnects the session under the assumption that the server is broken. To avoid breaking such clients, you'd probably need some way for clients to warn the server if they are prepared to receive more than the old max (similar to how we had to add VIR_TYPED_PARAM_STRING_OKAY as a way for clients to tell the server that they were prepared to handle typed strings being returned).  Basically, any time you change the RPC to allow more data to be returned than what was previously possible, the server should not return that additional data unless the client has negotiated that it is aware of the additional data. >> v0.9.10 patch client talk to v0.9.10 pre-patch server No problem for the client.  The server will never successfully return more than 256 names.  However, if the client requests more than 256 names, I'm not sure whether the server will silently truncate to 256 or whether it will return an RPC error because it was unable to provide the reply. > > And for comparison > >   v0.9.10 pre-patch client talk to v0.9.10 pre-patch server Should be the same behavior as a v0.9.10-patch client talking to a pre-patch server - you can't successfully send more than 256 names, but I'm not sure how the server will react if the client requests too many names.  Actually, it might be slightly different - the client might reject the request up front without even contacting the server. > > Obviously for > >   v0.9.10 patch client talk to v0.9.10 patch server > > I'd expect "just works" :-) Of course, if both sides are prepared to handle the new RPC protocol, it should just work. -- Eric Blake   eblake(a)redhat.com    +1-919-301-3266 Libvirt virtualization library http://libvirt.org