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Re: [Qemu-devel] [PATCH v0 00/21]: Monitor: improve handlers error handl

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH v0 00/21]: Monitor: improve handlers error handling
Date: Thu, 11 Feb 2010 08:04:42 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20091209 Fedora/3.0-4.fc12 Lightning/1.0pre Thunderbird/3.0

On 02/10/2010 07:49 PM, Luiz Capitulino wrote:
  Hi there,

  When I started converting handlers to the QObject style, I thought that
returning an error code wouldn't be needed. That is, we have an error object
already, so if the handler returns the error object it has failed, otherwise
it has succeeded.

  This was also very convenient, because handlers have never returned an error
code, and thus it would be easier to add a call to qemu_error_new() in the
right place instead of returning error codes.

  Turns out we need both. Actually, I should not have abused the error object
this way because (as Markus says) this is too fragile and we can end up
reporting bogus errors to clients (among other problems).

  The good news is that it's easy to fix.

  All we have to do is to change cmd_new() (the handler callback) to return an
error code and convert existing QObject handlers to it. This series does that
and most of the patches are really straightforward conversions.

  Additionally, Markus has designed an excellent debug mechanism for QMP, which
is implemented by the last patches in this series, and will allow us to catch
important QObject conversion and error handling bugs in handlers.

Instead of returning -1, would it make more sense to return an error object? If fact, why not drop ret_data as a passed in parameter, and just always return either the result or an error object.


Anthony Liguori


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