Re: The issue about adding multipath device's targets into qemu-pr-helper's namespace

Hi all, I have a namespace question about passthrough disk(multipath device). In case of enabling namespace and cgroups in qemu.conf, The target(s) of the multipath device won't be added into qemu-pr-helper's namespace under certain situation, It causes the PERSISTENT RESERVE command failure in guest.

While user starts a vm, To build namespace, The qemuDomainSetupDisk() will be invoked via threadA(this thread id will be the qemu's pid), To build cgroup, The qemuSetupImagePathCgroup() will be invoked via threadB. Both of the functions invoke the virDevMapperGetTargets() trying to parse a multipath device to target paths string, Then fill the targetPaths[]. The issue I experienced is: After libvirtd started, Everything works well for the first booted vm which has the passthrough multipath device. But If I shut it down & start it again, OR keep it running & start another vm which has other passthrough multipath device, Then the target(s) of the fresh started vm won't be added into the related qemu-pr-helper's namespace and it causes PERSISTENT RESERVE command failure in the corresponding guest. I digged into code, In this situation, The targetPaths[] in qemuDomainSetupDisk() won't be filled, it keeps NULL after virDevMapperGetTargets() returns. The virDevMapperGetTargets doesn't fill targetPaths[] because the dm_task_run() of libdevmapper returns 0 with errno 9(Bad file descriptor). So far, I don't understand why the dm_task_run() return 0 in this situation. BTW, The virDevMapperGetTargets() can always successfully fill the targetPaths[] in qemuSetupImagePathCgroup().