Thanks for the reply. I am trying to use the tracing with qemu-io as suggested in docs/tracing.txt. I did the following steps:
1. Configure and make with simple backend 2. Create a set of events I am interested in (/tmp/events) 3. Now I am running the qemu-iotests by adding T= /tmp/events to test 001 testcase (file read path only). It runs and generates a trace-xxxxx file. However, the file just has a couple of lines in it in binary. 4. When I pass it through simpletrace.py nothing happens. Can you tell me if I missed some step or something else needs to be done. Thanks for your help. Aayush On Wed, May 1, 2013 at 2:30 AM, Stefan Hajnoczi <stefa...@gmail.com> wrote: > On Mon, Apr 29, 2013 at 10:02:34AM -0700, aayush gupta wrote: > > I am trying to understand the IO paths in QEMU (which I understand > emulates > > IO for KVM) to have a better idea of how it works and get a clear picture > > of how I can trap all read/write requests being issued by the VM in the > > QEMU block layer for a project that I am working on. > > > > For example, lets say that we use QCOW2 image format for VMs. Looking > into > > the code, I was able to track the requests as follows: > > > > bdrv_read() -> bdrv_rw_co() -> bdrv_rw_co_entry() -> bdrv_co_do_readv() > -> > > this calls into driver specific functions > > Emulated devices typically use bdrv_aio_readv() instead of the > synchronous bdrv_read() function. bdrv_read() would block the guest > until the disk operation completes. > > The model is: > > Storage controllers (IDE, SCSI, virtio, etc) are emulated by QEMU in > hw/. The storage controller has a pointer to a BlockDriverState, which > is the block device. > > BlockDriverStates can form a tree. For example, a qcow2 file actually > involves a raw file BlockDriverState and the qcow2 format > BlockDriverState. The storage controller has a pointer to the qcow2 > format BlockDriverState. The qcow2 code invokes I/O operations on its > bs->file field, which will be the raw file BlockDriverState. > > This abstraction makes it possible to use qcow2 on top of a Sheepdog > volume, for example. > > Also, take a look at docs/tracing.txt. There are pre-defined trace > events for block I/O operations. This may be enough to instrument what > you need. > > Stefan >
