On Thu, Nov 24, 2011 at 5:31 AM, Daniel Veillard <veill...@redhat.com> wrote: > On Wed, Nov 23, 2011 at 09:04:50AM -0700, Eric Blake wrote: >> On 11/23/2011 07:48 AM, Stefan Hajnoczi wrote: >> > This means that virDomainBlockJobAbort() returns to the client without >> > a guarantee that the job has completed. If the client enumerates jobs >> > it may still see a job that has not finished cancelling. The client >> > must register a handler for the BLOCK_JOB_CANCELLED event if it wants >> > to know when the job really goes away. The BLOCK_JOB_CANCELLED event >> > has the same fields as the BLOCK_JOB_COMPLETED event, except it lacks >> > the optional "error" message field. >> > >> > The impact on clients is that they need to add a BLOCK_JOB_CANCELLED >> > handler if they really want to wait. Most clients today (not many >> > exist) will be fine without waiting for cancellation. >> > >> > Any objections or thoughts on this? >> >> virDomainBlockJobAbort() thankfully has an 'unsigned int flags' >> argument. For backwards-compatibility, I suggest we use it: >> >> calling virDomainBlockJobAbort(,0) maintains old blocking behavior, and >> we document that blocking until things abort may render the rest of >> interactions with the domain unresponsive. >> >> The new virDomainBlockJobAbort(,VIR_DOMAIN_BLOCK_JOB_ABORT_ASYNC) would >> then implement your new proposed semantics of returning immediately once >> the cancellation has been requested, even if it hasn't been acted on yet. >> >> Maybe you could convince me to swap the flags: have 0 change semantics >> to non-blocking, and a new flag to request blocking, where callers that >> care have to try the flag, and if the flag is unsupported then they know >> they are talking to older libvirtd where the behavior is blocking by >> default, but that's a bit riskier. > > Agreed, I would rather not change the current call semantic, > but an ASYNC flag would be a really good addition. We can document > the risk of not using it in the function description and suggest > new applications use ASYNC flag.
Yep, that's a nice suggestion and solves the problem. Stefan
