On Wed, Sep 28, 2011 at 3:23 PM, Sinha, Ani <ani.si...@tellabs.com> wrote: > > On Sep 28, 2011, at 1:51 AM, Stefan Hajnoczi wrote: > >> On Wed, Sep 28, 2011 at 3:01 AM, Sinha, Ani <ani.si...@tellabs.com> wrote: >>> >>> On Sep 27, 2011, at 12:17 AM, Stefan Hajnoczi wrote: >>> >>>> On Mon, Sep 26, 2011 at 07:16:56PM -0500, Sinha, Ani wrote: >>>>> I am using the virtqueue (virtqueue_pop, virtqueue_push etc) in the >>>>> emulated mode (non-kvm mode) from an IO thread (a separate thread >>>>> different from main QEMU thread). What I am observing is that the >>>>> virtqueue memory seems to get corrupt. Either qemu crashes while >>>>> performing virtqueue_push() (virtqueue_push() -> virtqueue_fill() >>>>> ->bring_used_idx()->lduw_phys()->qemu_get_ram_ptr()->"bad ram offset") or >>>>> crashes when the guest accesses a bad memory while using virtqueue. Now >>>>> this never ever happens when I run QEMU in KVM mode (/dev/kvm present) OR >>>>> when I use my functions from within the main qemu thread. I am unable to >>>>> figure out why this is happening. I have looked into my code over and >>>>> over again and I can't seem to explain this behavior. Can any of you guys >>>>> give me any inkling? >>>> >>>> QEMU is not thread-safe in general. It uses a big lock to protect most >>>> of its internal state. >>> >>> >>> I see. So may be I should do something like qemu_set_fd_handler(fd, …) >>> where fd is a pipe and the handler does the virtqueue_push() etc? >>> Now my question is, is it safe to do elem = virtqueue_pop(vq) from main >>> event loop, then so some work on the elem popped out in an worker thread >>> and then at some later point do a virtqueue_push(vq, elem) from that >>> handler (which is called by main_loop() ->main_loop_wait())? In other >>> words, the vq reference is being used from the main event loop at two >>> different points from two different functions but not in a contiguous >>> fashion within the same function. >> >> Yes but do you need a helper thread? Most of QEMU is based on >> qemu_set_fd_handler() and callbacks, including for host network and >> disk I/O. If you follow the way QEMU does things it should be >> easiest. > > I need a helper thread to do blocking IO. The device IOCTLS are inherently > blocking, unfortunately.
posix-aio-compat.c already implements a threadpool. It is geared towards using the QEMU block layer (BlockDriverState) but the pure ioctl codepath can be used without a BlockDriverState by passing NULL. So this could save you some effort, check out paio_submit(). Stefan
