Re: [Qemu-devel] [PATCH] block: change default of .has_zero_init to 0

[Kevin Wolf]

Am 28.06.2013 um 10:25 hat Peter Lieven geschrieben:
> On 28.06.2013 10:20, Kevin Wolf wrote:
> >Am 28.06.2013 um 10:16 hat Peter Lieven geschrieben:
> >>On 28.06.2013 10:06, Kevin Wolf wrote:
> >>>Am 27.06.2013 um 15:52 hat Peter Lieven geschrieben:
> >>>>.has_zero_init defaults to 1 for all formats and protocols.
> >>>>
> >>>>this is a dangerous default since this means that all
> >>>>new added drivers need to manually overwrite it to 0 if
> >>>>they do not ensure that a device is zero initialized
> >>>>after bdrv_create().
> >>>>
> >>>>if a driver needs to explicitly set this value to
> >>>>1 its easier to verify the correctness in the review process.
> >>>>
> >>>>during review of the existing drivers it turned out
> >>>>that ssh and gluster had a wrong default of 1.
> >>>>both protocols support host_devices as backend
> >>>>which are not by default zero initialized. this
> >>>>wrong assumption will lead to possible corruption
> >>>>if qemu-img convert is used to write to such a backend.
> >>>>
> >>>>a similar problem with the wrong default existed for
> >>>>iscsi mose likely because the driver developer did
> >>>>oversee the default value of 1.
> >>>>
> >>>>Signed-off-by: Peter Lieven <address@hidden>
> >>>>---
> >>>>  block.c               |    8 +++++++-
> >>>>  block/qcow.c          |    1 +
> >>>>  block/qcow2.c         |    1 +
> >>>>  block/qed.c           |    1 +
> >>>>  block/raw-posix.c     |   10 +---------
> >>>>  block/raw-win32.c     |    7 +------
> >>>>  block/rbd.c           |    1 +
> >>>>  block/sheepdog.c      |    1 +
> >>>>  block/vdi.c           |    1 +
> >>>>  block/vmdk.c          |    1 +
> >>>>  include/block/block.h |    1 +
> >>>>  11 files changed, 17 insertions(+), 16 deletions(-)
> >>>You forgot cow, which is also a simple case that can be handled in this
> >>>patch.
> >>ups.
> >>>vpc is still easy, but a bit more complicated than a constant return 1,
> >>>because it depends on the subformat whether a new image will inherit the
> >>>has_zero_init property from the underlying storage or whether it always
> >>>produces zeros (for VHD_FIXED type images, it's basically raw + footer).
> >>>I'll send a separate patch for this.
> >>shall I leave this to the new 0 default until your patch is ready?
> >Yes, please leave vpc alone. I guess my patch will be queued before
> >yours anyway. ;-)
> once v2 is ready and noone has objections maybe you can put it in your queue? 
> ;-)

Sure. I'm going to send a pull request today, so it would be good to
have v2 of this patch soon. (Otherwise it would have to wait for
Stefan's pull request probably next Friday)

Kevin