Am 12.07.2014 um 00:23 hat Max Reitz geschrieben: > Currently, the field "growable" in a BDS is set iff the BDS is opened in > protocol mode (with O_BDRV_PROTOCOL). However, not every protocol block > driver allows growing: NBD, for instance, does not. On the other hand, > a non-protocol block driver may allow growing: The raw driver does. > > Fix this by correcting the "growable" field in the driver-specific open > function for the BDS, if necessary. > > Signed-off-by: Max Reitz <mre...@redhat.com>
I'm not sure I agree with bs->growable = true for raw. It's certainly true that the backend can technically provide the functionality that writes beyond EOF grow the file. That's not the point of bs->growable, though. The point of it was to _forbid_ it to grow even when it's technically possible (non-file protocols weren't really a thing back then, apart from vvfat, so the assumption was that it's always technically possible). growable was introduced with bdrv_check_request(), which is supposed to reject guest requests after the end of the virtual disk (and this fixed a CVE, see commit 71d0770c). You're now disabling this check for raw. I think we need to make sure that bs->growable is only set if it is opened for an image that has drv->requires_growing_file set and therefore not directly used by a guest. Well, except that with node-name a guest will be able to use any image in the chain... Might this mean that it's really a BlockBackend property? Kevin
