Re: [libvirt] [PATCH 1/2] snapshot: add REVERT_FORCE to API

On 10/04/2011 01:24 PM, Laine Stump wrote: Exactly. For example, libvirt 0.9.6 does not understand FORCE (and using it would error out with unrecognized flag bit), but just happens to revert to a snapshot created by 0.9.4 on the first call with flags == 0. Libvirt 0.9.7, in the same situation, will error out with the new error value when flags == 0, but with the new error, so that you know you can safely add FORCE. One other consideration is that 0.9.6 understands the new flag VIR_DOMAIN_SNAPSHOT_REVERT_RUNNING, which 0.9.4 did not understand, so blindly looking for the 'unknown flag bit' error is not unique enough to be the indication that we could remove the --force bit and retry, because that still won't resolve on an 0.9.4 server. My choice of --force handling thus seems to be the one most likely to work for 0.9.4, 0.9.6, and 0.9.7, so that the user can blindly type 'virsh snapshot-revert dom old-snapshot --force' and attempt the revert regardless of server version. Conversely, I still wanted 'virsh snapshot-revert' _without_ --force will work in as many situations as the server supports, and that if a server rejects the operation because force is required, the error message will be specific enough to mention that. This is a good thing, so that users don't have to blindly add '--force' and expose themselves to unnecessary risk; rather, they should only add --force after an explicit message says what force would solve, and deciding that the risk of forcing for that particular case is worth it. I'll wait for the 2/2 ack before applying this, then. -- Eric Blake eblake(a)redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org