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Re: [Qemu-block] Virtio-BLK/SCSI write requests and data payload checksu

From: Stefan Hajnoczi
Subject: Re: [Qemu-block] Virtio-BLK/SCSI write requests and data payload checksums
Date: Tue, 18 Dec 2018 09:34:44 +0000
User-agent: Mutt/1.10.1 (2018-07-13)

On Mon, Dec 17, 2018 at 04:19:53PM +0100, Peter Lieven wrote:
> Actually I don't know for sure that the address comes from the guest. In 
> theory it could be that
> the request from the guest was less than 4096 byte and Qemu just assigned a 
> bounce buffer
> to read the whole block and copied the relevant part to the guest. Can I see 
> from the
> address (0x7fa4354c0000) if it comes from Qemu or the guest?

Something like this:

$ awk '/rw-p/ { split($1, a, "-"); print $1, strtonum("0x" a[2]) - 
strtonum("0x" a[1])}' /proc/$(pgrep qemu)/maps
7f01d3e00000-7f0213e00000 1073741824 <-- this must be my 1 GB guest RAM!

Then you can check if the memory address falls within the guest RAM

By the way, if you use special memory options (like share=on), then you
may need to adjust the awk script since the mmap will look different.


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