Xen devel - May 2006 - [PATCH] suggested change in exception-handling style of user-space tools

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@hp.com>



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On Tue, May 23, 2006 at 10:20:21AM -0600, Daniel Miles wrote:
> 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.
Applied, thank you.  Patches for cleaning up the error handling and diagnosis
are always welcome, so feel free to send more!
> Singed-off-by: Daniel Miles <daniel.t.miles@hp.com>
I like the idea of a patch, gently burned around the edges ;-)

Ewan.


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