Am 26.10.2012 04:54, schrieb Dong Xu Wang: > On Thu, Oct 25, 2012 at 10:56 PM, Eric Blake <[email protected]> wrote: >> On 10/25/2012 07:36 AM, Dong Xu Wang wrote: >>> + >>> + 64 - 79: image file format >>> + Format of image file. It must be non-empty. It is >>> coded >>> + in free-form ASCII, and is not NUL-terminated. Zero >>> + padded on the right. >> >> [1]...here you claim that backing and image file format are mandatory >> (must not be empty). Shouldn't you allow the file format to be empty, >> in which case qemu will probe? And why do you even need image file >> format - isn't the whole point of add-cow to wrap a raw image file, or >> are you planning on also being able to wrap non-raw files? Are there >> other non-raw file formats that lack backing file support, where add-cow >> can be used to give it a backing file? >> > > Kevin or Stefan, can you give me some opinion? Thanks.
Yes, there are plenty of other block drivers that don't support backing files, either because their image format/protocol can't provide such information or just because it's not implemented in qemu today. Kevin
