On Wed, Nov 10, 2010 at 12:40 PM, Prasad Joshi <P.G.Joshi@xxxxxxxxxxxxxxxxxxxxx> wrote: >> From: Stefan Hajnoczi [stefanha@xxxxxxxxx] >> Sent: 10 November 2010 11:12 >> To: Prasad Joshi >> Cc: Keqin Hong; kvm@xxxxxxxxxxxxxxx >> Subject: Re: Unable to start VM using COWed image > > On Wed, Nov 10, 2010 at 10:08 AM, Prasad Joshi > <P.G.Joshi@xxxxxxxxxxxxxxxxxxxxx> wrote: >> Where can I get the code of the qemu-kvm program? >> I cloned the qemu-lvm git repository and compiled the code. But it looks like qemu-kvm program is not part of this code.-- > >> qemu-kvm.git contains the qemu-kvm codebase but the binary is built in >> x86_64-softmmu/qemu-system-x86_64. Distro packages typically rename >> it to qemu-kvm. > > Thanks Stefan for your reply. > > I guess you pointed out the problem in the first mail. QEMU places a restriction on location of the COWed file. The source image and COWed image should be in the same drectory. > > In my case the source image was in directory /var/lib/libvirt/images/ and the COWed image was in /home/prasad/Virtual directory. > While debuging the source code using gdb I realized this limitation. It would be good to fix this problem. I will see if I can solve this problem. This behavior is a feature. You chose to use a relative backing file path when you used qemu-img create -b <relative-path>. If you want an absolute path you need to use qemu-img create -b /home/prasad/Virtual/... (i.e. specify an absolute path instead of a relative path). > One more question on the same lines, > How does QEMU detect the file is COWed and the name of the file (not whole path) from it is COWed? COW support comes from the image file format that you choose. A qcow file is not just a raw image file like the kind you can dd from a real disk. Instead it has its own file format including a header and metadata for tracking allocated space. The header contains the name of the backing file. Stefan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
