Re: [libvirt] [Qemu-devel] [PATCH v4 0/7] file descriptor passing using pass-fd

Am 03.07.2012 20:21, schrieb Corey Bryant: > On 07/03/2012 02:00 PM, Eric Blake wrote: >> On 07/03/2012 11:46 AM, Corey Bryant wrote: >> >>> >>> Yes, I think adding a +1 to the refcount for the monitor makes sense. >>> >>> I'm a bit unsure how to increment the refcount when a monitor reconnects >>> though. Maybe it is as simple as adding a +1 to each fd's refcount when >>> the next QMP monitor connects. >> >> Or maybe delay a +1 until after a 'query-fds' - it is not until the >> monitor has reconnected and learned what fds it should be aware of that >> incrementing the refcount again makes sense. But that would mean making >> 'query-fds' track whether this is the first call since the monitor >> reconnected, as it shouldn't normally increase refcounts. > > This doesn't sound ideal. Yes, it's less than ideal. >> The other alternative is that the monitor never re-increments a >> refcount. Once a monitor disconnects, that fd is lost to the monitor, >> and a reconnected monitor must pass in a new fd to be re-associated with >> the fdset. In other words, the monitor's use of an fd is a one-way >> operation, starting life in use but ending at the first disconnect or >> remove-fd. > > I would vote for this 2nd alternative. As long as we're not introducing > an fd leak. And I don't think we are if we decrement the refcount on > remove-fd or on QMP disconnect. In fact, I believe this one is even worse. I can already see hacks like adding a dummy FD with invalid flags and removing it again just to regain control over the fdset... You earlier suggestion made a lot of sense to me: Whenever a new QMP monitor is connected, increase the refcount. That is, as long as any monitor is there, don't drop any fdsets unless explicitly requested via QMP.