Re: [Qemu-devel] Functions to intercept Disk IO information?

[Fam Zheng <famz@redhat.com>]

On Thu, 10/22 01:13, QuQ Edsel wrote:
> Hi,
> My friends and I were assigned a task to find out a point to insert a
> callback function to intercept Disk IO activities such as read/write a .txt
> file. Our final goal is to generate a report for target process/file 's
> Disk IO activities. We have QEMU 2.3 with KVM enabled. We have been looking
> for such a point for long...but not so capable of such a task.
> People who had this project last year done so with TEMU 1.0 (probably QEMU
> 0.9), and the implementation point they had is dma_buf_rw(). The
> information in their report shows pid, timestamps, disk sector, buffer size
> and write/read for a target file (I am not even sure if such information is
> meaningful or useful)
> Currently I have tried to printf in functions such as dma_buf_rw /
> dma_blk_io / bdrv_aio_readv...etc. to see if they print out message when I
> open/edit/save a .txt or .jpeg file. The first one just don't print at all,
> and the second and third one print a lot after booting up the guest....
> I can see that the dma_blk_io function call in ide_dma_cb (core.c) may be
> related because it prints as I have activities on files. However it also
> prints sometime when I am not doing any thing... so I not that certain
> about it. (and I don't know if write/read activities invoke such
> function..)

Yes, dma_buf_rw should handle all your I/O unless you're doing PIO. I think the
other activities you see when you're not doing anything is from guest system's
background tasks.

Thanks,
Fam

> 
> Is there a correct /better point to intercept disk IO information
> ?(especially for activities such as read/write a .file)
> Or what should I do to clearly get the needed information from Disk IO
> functions?
> I would be so grateful to have the information.
> Thank you.
> 
> The guest environment I have is 64bit Windows 7 with qcow2 image (not sure
> if relative)
>