----- Original Message -----
From: "Francesco Romani" <fromani@redhat.com> To: libvir-list@redhat.com Sent: Friday, July 4, 2014 6:44:07 PM Subject: Re: [libvirt] [RFC][scale] new API for querying domains stats
However, a question here about bulk APIs. One cornerstone of oVirt is shared storage (NFS, ISCSI...); another is qemu/kvm, and COW images are supported (probably even the default, need to check).
Due to storage being unavailable because a network outage, it happened that virDomainGetBlockInfo blocked beyond recover.
On such scenarios, how will a bulk API behave? There will be a timeout or something else?
It depends on the storage and the way it is configured. If NFS is mounted with 'hard' + 'nointr' any call libvirt makes to dead storage will get stuck in an uninterruptable sleep in kernel space. There's no way for libvirt to time out since by the very definition of 'hard' mount option it does not time out. If you mount with 'soft' then the calls libvirt makes will time out.
My bad, I worded poorly my question.
What I mean is: on top of what the kernel or QEMU (libnfs, libiscsi) does, there are plans for any additional mechanism/safeguard? (I guess no, I'm asking just to be sure).
Hi, maybe borderline offtopic, but still about blocking calls: We (VDSM/oVirt developers) are reviewing our usage of libvirt in sampling. Afer a (quick) inspection of the code, I believe the following calls cannot block due to FS/storage issues, as they do not need it in any way I'm quite confident about these * virDomainGetCPUStats: uses cgroups only (no FS/storage access) * virDomainInterfaceStats: uses /proc/net/dev (no FS/storage access) * virDomainGetVcpus: uses uses /proc and syscall for PCPU affinity (no FS/storage access) * virDomainSchedulerParameters: which uses cgroups (no FS/storage access) Not sure about this, but it looks to me they don't need to access FS/storage either: * virDomainGetVcpusFlags * virDomainGetMetadata Can please anyone confirm or deny? Thanks and best regards -- Francesco Romani RedHat Engineering Virtualization R & D Phone: 8261328 IRC: fromani