On 01/14/2016 05:12 AM, Daniel P. Berrange wrote: > On Thu, Jan 14, 2016 at 10:51:47AM +0100, Jiri Denemark wrote: >> On Wed, Jan 13, 2016 at 16:25:14 +0100, Martin Kletzander wrote: >>> On Wed, Jan 13, 2016 at 10:18:42AM +0000, Richard W.M. Jones wrote: >>>> As people may know, we frequently encounter errors caused by libvirt >>>> when running the libguestfs appliance. >>>> >>>> I wanted to find out exactly how frequently these happen and classify >>>> the errors, so I ran the 'virt-df' tool overnight 1700 times. This >>>> tool runs several parallel qemu:///session libvirt connections both >>>> creating a short-lived appliance guest. >>>> >>>> Note that I have added Cole's patch to fix https://bugzilla.redhat.com/1271183 >>>> "XML-RPC error : Cannot write data: Transport endpoint is not connected" >>>> >>>> Results: >>>> >>>> The test failed 538 times (32% of the time), which is pretty dismal. >>>> To be fair, virt-df is aggressive about how it launches parallel >>>> libvirt connections. Most other virt-* tools use only a single >>>> libvirt connection and are consequently more reliable. >>>> >>>> Of the failures, 518 (96%) were of the form: >>>> >>>> process exited while connecting to monitor: qemu: could not load kernel '/home/rjones/d/libguestfs/tmp/.guestfs-1000/appliance.d/kernel': Permission denied >>>> >>>> which is https://bugzilla.redhat.com/921135 or maybe >>>> https://bugzilla.redhat.com/1269975. It's not clear to me if these >>>> bugs have different causes, but if they do then potentially we're >>>> seeing a mix of both since my test has no way to distinguish them. >>>> >>> >>> It looks to me as the same problem. And as the same problem we were >>> talking about bunch of time and, apparently, didn't get to a conclusion. >>> >>> For each of the kernels, libvirt labels them (with both DAC and selinux >>> labels), then proceeds to launching qemu. If this is done parallel, the >>> race is pretty obvious. Could you remind me why you couldn't use >>> <seclabel model='none'/> or <seclabel relabel='no'/> or something that >>> would mitigate this? If we cannot use this, then we need to implement >>> the <seclabel/> element for kernel and initrd. >> >> Hmm, can't we just label kernel and initrd files the same way we label >> <shareable/> disk images, i.e., non-exclusive label so that all QEMU >> process can access them and avoid removing the label once a domain >> disappears? > > We actually should treat it in the same way as <readonly/> disks, > and give it a shared read-only label. And indeed we *do* that. > > The difference comes in the restore step - where we blow away the > readonly label and put it back to the original. For disks we never > restore readonly/shared labels, but for kernels we do. If we just > kill the restore step for kernels too, we should be fine AFAICT. > Indeed I forgot we don't restore labels on readonly/shareable disks.. certainly kernel/initrd should match that. - Cole -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list