On Thu, Sep 12, 2013 at 01:27:32PM +0200, Jack Wang wrote: > Hi all, > > We're using qemu export md-raid to guest OS, and we saw deadlock on > MD(which is already fixed by Neil), please see thread below: > > http://marc.info/?l=linux-raid&m=137894040228125&w=2 > > As Neil suggested it would be good for userspace applications to call > open() with O_EXCL flag, to avoid such MD hanging problems at the begining. > > And we checked qemu, it looks it doesn't include O_EXCL flag when open > block device. > > After search in the mail list we found there are a similar discussion: > > https://lists.nongnu.org/archive/html/qemu-devel/2011-04/msg00722.html > > > To O_EXCL or not to O_EXCL open host_cdrom > > Which looks prefer enable O_EXCL, but I checked latest qemu tree, there > no such code, could anyone give comments on this?
Continuing from that discussion, I think the shared CD-ROM case is something we must avoid breaking. It worked in the past so it shouldn't break in a new QEMU version. Kevin: Do you think we should add an option to the host_device BlockDriver that sets the O_EXCL open flag? That way users and new libvirt can use O_EXCL for host block devices. The simpler alternative is to always use O_EXCL for non-CDROM host devices. Simple patch, no configuration required, but it means we continue to lack O_EXCL on CD-ROMs. Stefan
