Re: [libvirt] [PATCH v2 04/11] qemu: handle host usb device add/del udev events

On 16.09.2019 11:26, Peter Krempa wrote: > On Mon, Sep 09, 2019 at 14:33:07 +0300, Nikolay Shirokovskiy wrote: >> Now when code handling attaching/detaching usb hostdev is appropriately >> changed use it to handle host usb device udev add/del events. >> >> Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy(a)virtuozzo.com&gt; >> --- >> src/qemu/Makefile.inc.am | 2 + >> src/qemu/qemu_conf.h | 3 + >> src/qemu/qemu_domain.c | 2 + >> src/qemu/qemu_domain.h | 2 + >> src/qemu/qemu_driver.c | 351 ++++++++++++++++++++++++++++++++++++++- >> 5 files changed, 359 insertions(+), 1 deletion(-)

> > Is this executed from the event loop thread? If yes we can't do this as > qemuUdevUSBHandleEvent is taking domain locks and thus potentially > waiting indefinitely for any stuck VM. Yes, this is executed in the event loop thread. But I guess we can take domain lock here as this lock is intended to be grabbed only for short periods of time by design (as stated in THREADS.txt). There are a lot of qemu event handlers that grab domain lock (qemuProcessHandleMonitorEOF for example). AFAIK we use offloading to thread pool if we need to start a job which can take long time because of already running job. And this is offloading is done in qemuUdevUSBHandleEvent.