Re: KVM Block Device Driver

Wolfgang Richter
2013-08-14T15:02:37Z

On Wed, Aug 14, 2013 at 10:43 AM, Spensky, Chad - 0559 - MITLL
<chad.spensky@ll.mit.edu> wrote:
> Wolf,
>
> We're able to get all of the meta data just fine.

I assume by meta-data you mean (essentially) "function" call
parameters within QEMU as to the (1) location of the write on disk,
and (2) the amount of data being written out (in bytes).

> However it seems that
> the actual content of the read/write seems to be wrong some of the time.

That's very odd, I'm pretty sure I never had that bug (although I
might silently have it!).

I did occasionally observe a kernel accidentally writing out kernel
buffers that hadn't been cleared to disk (guest kernel) :-)

> The first 2 sectors seem to always be correct, however on some writes, the
> data that we traced does not match up with the data we are actually seeing
> in the .img file for the guest on disk.

Are you certain you're getting every write? Sometimes things might be
written to rapidly in succession?

How are you obtaining the shadow copy of the write stream (maybe there
was earlier stuff in this thread I should read up on)?

--
Wolf