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Date: Thu, 27 Jun 2013 16:43:17 +0200
Message-ID: <CAJSP0QXDRcDGPtxkVMQ2ddAtBa4bfwQ==H_u0X5zFymcwmwhBQ@mail.gmail.com>
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] PVFS2 Block Driver Support
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To: Timothy Scott <tscott2@clemson.edu>
Cc: qemu-devel <qemu-devel@nongnu.org>

On Thu, Jun 27, 2013 at 4:25 PM, Timothy Scott <tscott2@clemson.edu> wrote:
> I am working on adding block driver support for PVFS2 that will allow images
> stored on PVFS2 systems to bypass the kernel module and hopefully improve
> performance significantly.

What performance bottlenecks are you seeing in the kernel which you
can bypass from QEMU userspace?

> Can you please advise on a couple of issues:
>   - Should qcow2 and other optimizing formats function when using pvfs2 as a
> transport/block layer?  ie 'qemu-img create -f qcow2 pvfs2:foo.img 10g'

qcow2 works on top of any "protocol" and it should work on top of
PVFS2.  QED does not and other formats may or may not (VHDX, VMDK,
etc).

>   - Are there any debugging tools or compile flags that are recommended for
> use in QEMU?  I am currently hacking around with gdb and having trouble
> navigating through much of the code.

You may find trace events useful, see docs/tracing.txt.

>   - Is there currently a testing suite/procedure for verifying new block
> drivers?

There is a test suite in tests/qemu-iotests/.  You will need to add
support for PVFS2, see how NBD and other protocols were added.

Stefan