On 11/29/2009 12:45 AM, Chris Webb wrote: > MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp> writes: > >> Even read-only access is not allowed while another qemu is doing >> write access. However, there is no problem about your patch, I guess. >> >> It is because Sheepdog allow us to clone images only from >> snapshot images. It means a backing image is always read-only. >> If users specify writable Sheepdog VDI as a backing image, >> qemu-img returns error. > > What about the case of (for example) a qcow2 file backed by a Sheepdog > image? Is that also restricted to be a snapshot image (and therefore safe) > or is there a potential problem there? Yes, in this case, a backing Sheepdog image is restricted to a snapshot image, too. However, taking other formats into account, bdrv_claim may be required even when opening as read-only. It is because qcow2 cannot prevent other VMs write data to an opened backing image. If so, bdrv_claim need more arguments such as open flags to notify the opened image is read-only or not, right? Regards, MORITA Kazutaka |