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

[Peter Lieven <pl@kamp.de>]

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 <pl@kamp.de>
>>>> ---
>>>>   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? ;-)

Peter