[Xen-devel] [PATCH] suggested change in exception-handling style of user-space tools

[Daniel Miles <daniel.t.miles@xxxxxx>]

In the tools/python/xen/xm directory, main.py has good error messages
that let the user know what failed; the other 'sub-command' classes
don't always have such good messages which can lead to some inexplicable
failures by the user-space tools.

Standard practice is to except each error by type and react accordingly
but in case the programmer does not anticipate a type of exception,
standard practice is to put in a catch-all exception handler that
excepts an 'Exception' object. Often in this case, the system will print
out the exception and exit.

If a sub-command excepts an 'Exception' object and the error is not
specific to that sub-command, it should pass the exception up for main
to handle. Especially in light of the fact that there is already a broad
collection of good error messages in main, I believe that this will lead
to better code re-use in the form of a one-stop-shop for error messages.
In this patch I've changed only one of the general case exception
handlers in one of the sub-commands (xm create) as a test-balloon to see
if the xen community will accept future patches of this type.

Singed-off-by: Daniel Miles <daniel.t.miles@xxxxxx>

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