On Mon, Oct 24, 2011 at 10:31:48PM -0200, Luiz Capitulino wrote: > On Mon, 24 Oct 2011 19:29:37 +0200 > Alon Levy <al...@redhat.com> wrote: > > > On Mon, Oct 24, 2011 at 01:45:16PM -0200, Luiz Capitulino wrote: > > > On Mon, 24 Oct 2011 17:13:14 +0200 > > > Gerd Hoffmann <kra...@redhat.com> wrote: > > > > > > > On 10/24/11 14:02, Alon Levy wrote: > > > > > Make screen_dump monitor command an async command to allow next for > > > > > qxl > > > > > to implement it as a initiating call to red_worker and completion on > > > > > callback, to fix a deadlock when issueing a screendump command via > > > > > libvirt while connected with a libvirt controlled spice-gtk client. > > > > > > > > Approach looks reasonable to me. Patch breaks the build though, you've > > > > missed a bunch of screen_dump functions in non-x86 targets. > > > > > > There are two problems actually. > > > > > > The first one is that changing an existing command from synchronous > > > to asynchronous is an incompatible change because asynchronous commands > > > semantics is different. For an example of possible problems please > > > check: https://bugzilla.redhat.com/show_bug.cgi?id=623903. > > > > > > The second problem is that the existing asynchronous interface in the > > > monitor is incomplete and has never been used for real. Our plan is to > > > use QAPI's async support, but that has not landed in master yet and iirc > > > there wasn't consensus about it. I also think it's a bit late for its > > > inclusion in 1.0 (and certainly not a candidate for stable). > > > > > > If all you need here is to delay sending the response, then maybe the > > > current interface could work (although I honestly don't trust it and > > > regret not having dropped it). Otherwise our only choice would be to > > > work on getting the QAPI async support merged. > > > > My problem is that the io thread keeps the global mutex during the wait, > > that's why the async monitor is perfect for what I want - this is > > exactly what it does. > > Let's not mix internal implementation details with what we want as > an external interface. > > Can't you just make a vga_hw_screen_dump() specific callback? >
I don't understand how that would help - if the monitor command doesn't return (normal sync operation) then the mutex is never dropped, and any callback won't change that. On the other hand, thinking a bit about the reference to 623903 baloon bug, I don't see a problem: the change doesn't affect the semantics for any other device except qxl, which I've tested. For any other device, the only difference is that instead of: do_screen_dump call device specific implementation return It becomes do_screen_dump call device specific implementation (not qxl) callback called (always - not conditional, no one stores it except qxl) return > > I haven't looked at QAPI async support, but I > > understand it's a bit in the future. > > Yes, it's not for the immediate term.
