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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: Wed, 08 Jun 2011 07:59:33 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10

On 06/06/2011 10:30 AM, Luiz Capitulino wrote:
On Mon, 6 Jun 2011 16:27:55 +0100
"Daniel P. Berrange"<address@hidden>  wrote:

On Mon, Jun 06, 2011 at 08:08:51AM -0500, Anthony Liguori wrote:
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.

Anything QEMU writes to stderr or stdout gets recorded in a
per-VM logfile already at /var/log/libvirt/qemu/$GUESTNAME.log

I can submit a patch to write this info to stderr (in case we don't do that
yet).

That's not terribly friendly to users though.

We need something akin to a -log stderr so that normal users can redirect to a file. I think libvirt would only need to add this to their invocation and everything would Just Work.

Regards,

Anthony Liguori



Regards,
Daniel






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