Am 09.07.2012 17:23, schrieb Corey Bryant: >>> I think it would cause fds to sit on the monitor >>> until refcount gets to zero (monitor disconnects). Here's an example >>> without the in-use flag: >>> >>> 1. client calls 'add-fd', qemu is now tracking fd=4 in fdset1 with >>> refcount of 1 (incremented because of monitor reference); fd=4's remove >>> flag is initialized to off >>> 2. client calls 'device-add' with /dev/fdset/1 as the backing filename; >>> qemu_open() increments the refcount of fdset1 to 2 >>> 3. client crashes, so all fdsets are visited; fd=4 had not yet been >>> passed to 'remove-fd', so it's remove flag is off; refcount for fdset1 >>> is decremented to 1; fd=4 is left open because it is still in use by the >>> block device (refcount is 1) >>> 4. client re-establishes QMP connection, refcount for fdset1 is >>> incremented to 2; 'query-fds' lets client learn about fd=4 still being >>> open as part of fdset1 >>> 5. client calls 'remove-fd fdset=1 fd=4'; qemu turns on remove flag for >>> fd=4; but fd=4 remains open because refcount of fdset1 is 2 >> >> It also decreases the reference count because the monitor doesn't use it >> any more. > > I don't think that will work because refcount is for the entire fdset. > So we can't decrement the refcount for every fd that is removed from the > fdset. > > I think it is much simpler if we only increment refcount for an fdset on > qemu_open, and only decrement refcount on qemu_close. Ah right... So this would only work if we had explicit fdset-create/close commands, where the former would increase the refcount and the latter decrease it (fdset-open would be optional but I like symmetry) Maybe we need (or want) that anyway, but I need to think more about it first. >>> 6. qemu_close is called for fd=4; refcount for fdset1 is decremented to >>> 1; fd=4 remains open because monitor still references fdset1 (refcount >>> of fdset1 is 1) >> >> So here the refcount becomes 0 and the fdset is closed. >> > >>> 7. Sometime later.. QMP disconnects; refcount for fdset is decremented >>> to zero; fd=4 is closed >> >> The only question that is a bit unclear to me is whether a remove-fd on >> one monitor drops the refcount only for this monitor or for all >> monitors. However, both options can be implemented without additional >> flags or counters. > > Before we go back and forth on this thread, would you mind taking a look > at the last email I sent to Luiz? It includes all the design points > that I'm currently working from. I think it's a good level set and we > can work off that thread if there are still any issues. Ok, I'll have a look. Kevin -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list