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Re: [Qemu-devel] QMP: RFC: I/O error info & query-stop-reason


From: Anthony Liguori
Subject: Re: [Qemu-devel] QMP: RFC: I/O error info & query-stop-reason
Date: Mon, 06 Jun 2011 08:08:51 -0500
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On 06/06/2011 04:25 AM, Kevin Wolf wrote:
Am 02.06.2011 20:09, schrieb Luiz Capitulino:
I'm ok with either way. But in case you meant the second one, I guess
we should make "reason" a dictionary so that we can group related
information when we extend the field, for example:

   "reason": { "no space": false, "no permission": true }

Splitting up enums into a number of booleans looks like a bad idea to
me. It makes things more verbose than they should be, and even worse, it
implies that more than one field could be true.

I agree.  What I had suggested was to not have a reason at all.


If this new schema thing doesn't support proper enums, that's something
that should be changed.

It does BTW.


Why would we ever have "no permission"?

It's an I/O error. I have a report from a developer who was getting
the BLOCK_IO_ERROR event and had to debug qemu to know the error cause,
it turned out to be no permission.

And I want to add that it's a PITA to handle bug report when the only
message you get from qemu is "something went wrong". Sorry, that's not
useful at all. I want to see the real error reason (and at least for
debugging this means, I want to see the errno value/string).

Finding out that it was -EACCES in fact cost me (and QA who ran into the
problem) much more time than it should have. It's simply too much that
you need to attach gdb to find out what really happened.

You want a log file and you want libvirt to actually let QEMU write to a log file.

Since we already have trace points, could we have a white list of trace points that are written to a log file by default?

QMP is a stable interface that we have to maintain forever. We can write whatever we want to a log file and change what gets written at will.

Regards,

Anthony Liguori

Kevin





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