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Re: [Qemu-devel] [PATCH 3/4] QError: Don't abort on multiple faults

From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH 3/4] QError: Don't abort on multiple faults
Date: Fri, 05 Feb 2010 15:21:13 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)

Markus Armbruster <address@hidden> writes:

> Luiz Capitulino <address@hidden> writes:
>> Ideally, Monitor code should report an error only once and
>> return the error information up the call chain.
>> To assure that this happens as expected and that no error is
>> lost, we have an assert() in qemu_error_internal().
>> However, we still have not fully converted handlers using
>> monitor_printf() to report errors. As there can be multiple
>> monitor_printf() calls on an error, the assertion is easily
>> triggered when debugging is enabled; and we will get a memory
>> leak if it's not.
>> The solution to this problem is to allow multiple faults by only
>> reporting the first one, and to release the additional error objects.
> I want this badly.
> [...]

Let me elaborate a bit.  While this patch is a much wanted improvement,
what I *really* want is something else.

Right now, we have 41 uses of qemu_error_new().  We still have >300 uses
of monitor_printf(), many of them errors.  Plus some 100 uses of
qemu_error(), which boils down to monitor_printf() when running within a
monitor.  Not to mention >1000 uses of stderr.

To convert a monitor handler to QError, we have to make it report
exactly one error on every unsuccessful path, with qemu_error_new().
That's not too hard.  Then we have to ensure it does not call
monitor_printf() directly (not hard either) or indirectly (ouch).  I say
"ouch", because those prints can hide behind long call chains, in code
shared with other users.  Cleaning up all those stray prints will take

Without this patch, a stray print is fatal, unless it happens to be the
only one *and* there is no real error.

With this patch, we survive, but the UndefinedError triggered by the
stray print displaces any later real error.

What I really want is that stray prints do not mess with my real errors.

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