Re: [Qemu-devel] Tracking the VM making an IO request

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, Feb 10, 2016 at 12:35:54PM +0330, Aarian P. Aleahmad wrote:
> I'm a student, engaged in a project in which QEMU is a candidate to be used
> to make some studies about IO usage etc.
> I need to track the IO requests made to the block devices (e.g. HDD, SSD,
> etc.). I check the source code but I was confused. What I want to know is
> that when an IO request is made, find out that which on of the VMs has made
> that request. I'll thank you if you help me on this issue.

There are trace events that you can use.  See docs/tracing.txt and
trace-events.

virtio_blk_handle_write and virtio_blk_handle_read can be used if your
guest has virtio-blk.

The QEMU block layer also has trace events named bdrv_aio_*.

Or you could use blktrace(8) in the guest or on the host, depending on
how you've set up storage.

Finally, if you prefer you could set up an iSCSI or NBD target and
simply use Wireshark to record and analyze the I/O request patterns.

Stefan

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