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

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.

> 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.