Am 02.06.2011 20:09, schrieb Luiz Capitulino:
On Thu, 02 Jun 2011 13:00:04 -0500
Anthony Liguori<address@hidden> wrote:
On 06/02/2011 12:57 PM, Luiz Capitulino wrote:
On Wed, 01 Jun 2011 16:35:03 -0500
Anthony Liguori<address@hidden> wrote:
On 06/01/2011 04:12 PM, Luiz Capitulino wrote:
Hi there,
There are people who want to use QMP for thin provisioning. That's, the VM is
started with a small storage and when a no space error is triggered, more space
is allocated and the VM is put to run again.
QMP has two limitations that prevent people from doing this today:
1. The BLOCK_IO_ERROR doesn't contain error information
2. Considering we solve item 1, we still have to provide a way for clients
to query why a VM stopped. This is needed because clients may miss the
BLOCK_IO_ERROR event or may connect to the VM while it's already stopped
A proposal to solve both problems follow.
A. BLOCK_IO_ERROR information
-----------------------------
We already have discussed this a lot, but didn't reach a consensus. My solution
is quite simple: to add a stringfied errno name to the BLOCK_IO_ERROR event,
for example (see the "reason" key):
{ "event": "BLOCK_IO_ERROR",
"data": { "device": "ide0-hd1",
"operation": "write",
"action": "stop",
"reason": "enospc", }
you can call the reason whatever you want, but don't call it stringfied
errno name :-)
In fact, just make reason "no space".
You mean, we should do:
"reason": "no space"
Or that we should make it a boolean, like:
"no space": true
Do we need reason in BLOCK_IO_ERROR if query-block returns this information?
True, no.
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.
If this new schema thing doesn't support proper enums, that's something
that should be changed.
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).