On Fri, Jul 26, 2019 at 12:58:58PM +0200, Max Reitz wrote: > On 26.07.19 11:04, Stefano Garzarella wrote: > > On Wed, Jul 24, 2019 at 07:12:31PM +0200, Max Reitz wrote: > >> No .bdrv_has_zero_init() implementation returns 1 if growing the file > >> would add non-zero areas (at least with PREALLOC_MODE_OFF), so using it > >> in lieu of this new function was always safe. > >> > >> But on the other hand, it is possible that growing an image that is not > >> zero-initialized would still add a zero-initialized area, like when > >> using nonpreallocating truncation on a preallocated image. For callers > >> that care only about truncation, not about creation with potential > >> preallocation, this new function is useful. > >> > >> Alternatively, we could have added a PreallocMode parameter to > >> bdrv_has_zero_init(). But the only user would have been qemu-img > >> convert, which does not have a plain PreallocMode value right now -- it > >> would have to parse the creation option to obtain it. Therefore, the > >> simpler solution is to let bdrv_has_zero_init() inquire the > >> preallocation status and add the new bdrv_has_zero_init_truncate() that > >> presupposes PREALLOC_MODE_OFF. > >> > >> Signed-off-by: Max Reitz <mre...@redhat.com> > >> --- > >> include/block/block.h | 1 + > >> include/block/block_int.h | 7 +++++++ > >> block.c | 21 +++++++++++++++++++++ > >> 3 files changed, 29 insertions(+) > >> > >> diff --git a/include/block/block.h b/include/block/block.h > >> index 50a07c1c33..5321d8afdf 100644 > >> --- a/include/block/block.h > >> +++ b/include/block/block.h > >> @@ -438,6 +438,7 @@ int bdrv_pdiscard(BdrvChild *child, int64_t offset, > >> int64_t bytes); > >> int bdrv_co_pdiscard(BdrvChild *child, int64_t offset, int64_t bytes); > >> int bdrv_has_zero_init_1(BlockDriverState *bs); > >> int bdrv_has_zero_init(BlockDriverState *bs); > >> +int bdrv_has_zero_init_truncate(BlockDriverState *bs); > >> bool bdrv_unallocated_blocks_are_zero(BlockDriverState *bs); > >> bool bdrv_can_write_zeroes_with_unmap(BlockDriverState *bs); > >> int bdrv_block_status(BlockDriverState *bs, int64_t offset, > >> diff --git a/include/block/block_int.h b/include/block/block_int.h > >> index 6a0b1b5008..d7fc6b296b 100644 > >> --- a/include/block/block_int.h > >> +++ b/include/block/block_int.h > >> @@ -420,9 +420,16 @@ struct BlockDriver { > >> /* > >> * Returns 1 if newly created images are guaranteed to contain only > >> * zeros, 0 otherwise. > >> + * Must return 0 if .bdrv_has_zero_init_truncate() returns 0. > >> */ > > > > Does it make sense to make sure of that in the bdrv_has_zero_init()? > > > > I mean something like this: > > > > int bdrv_has_zero_init(BlockDriverState *bs) > > { > > ... > > if (bs->drv->bdrv_has_zero_init && > > bs->drv->bdrv_has_zero_init_truncate) { > > return bs->drv->bdrv_has_zero_init_truncate(bs) && > > bs->drv->bdrv_has_zero_init(bs); > > } else if (bs->drv->bdrv_has_zero_init) > > return bs->drv->bdrv_has_zero_init(bs); > > } > > ... > > } > > I thought about it, but I didn’t like it because that would mean that > bdrv_has_zero_init() kind of differs from .bdrv_has_zero_init().
Ah right! And eventually a bug in .bdrv_has_zero_init() would be masked. So, Reviewed-by: Stefano Garzarella <sgarz...@redhat.com> Thanks, Stefano