CA-39745: watch /local/domain/%d/error/backend/vbd/%d/%d/error for informative errors such as "2 creating vbd structure". This prevents us timing out after 20 minutes if something goes wrong with a blkback device.
CA-39745: watch /local/domain/%d/error/backend/vbd/%d/%d/error for informative errors such as "2 creating vbd structure". This prevents us timing out after 20 minutes if something goes wrong with a blkback device.

A further patch will be needed to provide some decent error diagnosis.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

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