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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

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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