Re: [libvirt] [PATCH] esx: Improve blocked task detection and fix race condition

On Mon, Jul 26, 2010 at 03:12:25AM +0200, Matthias Bolte wrote: > esxVI_WaitForTaskCompletion can take a UUID to lookup the > corresponding domain and check if the current task for it > is blocked by a question. It calls another function to do > this: esxVI_LookupAndHandleVirtualMachineQuestion looks up > the VirtualMachine and checks for a question. If there is > a question it calls esxVI_HandleVirtualMachineQuestion to > handle it. > > If there was no question or it has been answered the call > to esxVI_LookupAndHandleVirtualMachineQuestion returns 0. > If any error occurred during the lookup and answering > process -1 is returned. The problem with this is, that -1 > is also returned when there was no error but the question > could not be answered. So esxVI_WaitForTaskCompletion cannot > distinguish between this two situations and reports that a > question is blocking the task even when there was actually > another problem. > > This inherent problem didn't surface until vSphere 4.1 when > you try to define a new domain. The driver tries to lookup > the domain that is just in the process of being registered. > There seems to be some kind of race condition and the driver > manages to issue a lookup command before the ESX server was > able to register the domain. This used to work before. > > Due to the return value problem described above the driver > reported a false error message in that case. > > To solve this esxVI_WaitForTaskCompletion now takes an > additional occurrence parameter that describes whether or > not to expect the domain to be existent. Also add a new > parameter to esxVI_LookupAndHandleVirtualMachineQuestion > that allows to distinguish if the call returned -1 because > of an actual error or because the question could not be > answered. > --- >  src/esx/esx_driver.c |   17 ++++++++++++++- >  src/esx/esx_vi.c     |   53 ++++++++++++++++++++++++++++++++++++------------- >  src/esx/esx_vi.h     |    7 ++++- >  src/esx/esx_vmx.c    |    4 +- >  4 files changed, 61 insertions(+), 20 deletions(-)  Thanks for the detailed explanations !  ACK, Daniel