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78 lines
3.6 KiB
Plaintext
78 lines
3.6 KiB
Plaintext
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Some links to relevant documentation
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====================================
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VI/vSphere API: http://www.vmware.com/support/developer/vc-sdk/visdk25pubs/ReferenceGuide/
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http://www.vmware.com/support/developer/vc-sdk/visdk400pubs/ReferenceGuide/
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VMX config: http://www.sanbarrow.com/vmx.html
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CPUID: http://www.sandpile.org/ia32/cpuid.htm
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Memory model: http://www.vmware.com/pdf/esx3_memory.pdf
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http://www.vmware.com/pdf/usenix_resource_mgmt.pdf
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Automatic question handling
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===========================
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What is a question in the ESX context?
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--------------------------------------
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The VI API contains methods that start tasks, for example PowerOnVM_Task(). Such
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tasks may be blocked by questions if the ESX host detects an issue with the
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virtual machine that requires user interaction.
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An example: If a virtual machine has a serial port that is realized via a file,
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the ESX host will ask a question on power-on of this virtual machine whether
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new content should be appended to this file or the file should be replaced.
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Until this question is answered the power-on task is blocked and the virtual
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machine won't get powered on.
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The ESX driver cannot prompt the user to answer a question, libvirt doesn't
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have an API for something like this. The VI API provides the AnswerVM() method
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to programmatically answer such questions. A question comes together with a list
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of possible answers. One of this answers is marked as the default one. For all
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questions I've seen so far the default answer is always a non-destructive one.
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There are two options how to handle a question that is blocking a task: either
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answer it automatically or report it as error and try to cancel the blocked
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task.
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The auto_answer query parameter defines how the driver should handle questions.
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Possible values are 0 for the report-error-and-try-to-cancel option and 1 for
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the automatic-answer option.
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How is automatic question handling implemented?
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-----------------------------------------------
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Before any new task is started the driver checks if there is a pending task
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blocked by a question. If automatic question handling is disabled the driver
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reports an error that includes the question and returns from the driver
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function. If automatic question handling is enabled the driver answers the
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question with the default answer and returns from the driver function.
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In both cases the actual desired task is not started. If the question was not
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answered the blocked task is still blocked and because task can't be executed
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in parallel in general it's of no use to start yet another task. If the
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question was answered the blocked task may already perform the desired action
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and one must wait for its completion, so it's of no use to start yet another
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task.
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If there is no question blocking a task or another pending task that had not
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finished yet the driver starts the desired task and waits for its completion.
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While polling for status updates of the task it also checks for question that
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may have been triggered by the current task and handles them according to the
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value of the auto_answer query parameter. If automatic question handling is
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enabled the driver answers the question with the default answer and continues
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polling for status updates. If automatic question handling is disabled the
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driver reports an error that includes the question, tries to cancel the blocked
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task and returns from the driver function.
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It tries to cancel the blocked task, but this may not be possible, because
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there are task like the power-on task that is marked as non-cancelable. So the
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driver may leave blocked tasks behind if automatic question handling is
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disabled.
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